I feel that those who hold this opinion must not have any athletic background, because with any scrutiny, it falls apart.
Although I'm not totally sold on this training method
To understand the issue with attempting to map this pithy expression onto lifting, one must understand that with non-lifting sports, weight training is not the competition itself, but purely a means to get stronger for one's sport. As such, we must understand that, with sports, we are dealing with two specific instances where effort is employed to improve performance.
We must not confuse one with the other. When one engages in practice, the intent is to rehearse the movement patterns in order to ingrain them into muscle memory. For example, when a basketball player practices free throws, they are practicing the mechanics of shooting the basketball with the intent of making it into the basket. In contrast, the intent of training is to improve the attributes of the player, not their mechanical skill. When one engages in training, they become bigger, stronger, faster, leaner, better conditioned, etc, while when one engages in practice, they become better.
This ultimately is the conflict that confuses lifting trainees, because in our mind, becoming better at lifting is equated to becoming stronger, but the reality is that these are two very different things. Two lifters could add 50lbs to their bench press, but one could have managed this because they become a better bencher, and the other could do so because they became a stronger bencher. Ideally, you will become both through your efforts, but in doing so it becomes necessary to know when you are practicing and when you are training.
The guy on the right may be a better fighter, but I wouldn't want to get hit by the one on the left
Not every lifting session is necessarily a practice session at the lift, and in many cases one can instead engage in training for the sake of not becoming a better lifter, but a stronger one. In these instances, it is the case that one may have technique on a lift that in no way mirrors their form on a competition lift, but is very much accomplishing the goal of making the trainee stronger at the lift.
Squats not to competition depth can be employed to overload the muscles involved in the lift to make them stronger. Touch and go bench presses can be used to overload the triceps. Touch and go deadlifts can be used to maintain tension in the lower back. Low bar squatters can squat high bar to develop their quads, and high bar squatters can squat low bar to develop their hamstrings.
Ok, no, shut up
The argument proposed that training this way will somehow develop poor muscle memory resorting in one failing in competition is again one that ignores athletes that employ weight training that compete in other sports. A football lineman will perform heavy squats with a barbell on their back from a standing position, even though said lineman will start a play on the line, in no way standing upright and moving straight up and down. Why is there no fear of this lineman falling back on "bad muscle memory" when it is their time to perform, yet when it comes to a lifter we give them far less credit? Do we assume that lifters are unable to distinguish between form used on a competition lift and form used on a training lift?
Additionally, if one is to practice how they play, why do we not demand that the lineman perform all of his weight training in full pads, after many explosive starts off the line, dehydrated, fatigued, most likely partially injured, with several 300lb men trying to tackle him? Once again, we understand that the point of either training or practice is to produce better results, and this necessitates creating an environment conducive toward this goal. A boxer does not learn the fundamentals of the sport while being mercilessly pummeled by a professional fighter, but instead is gradually taught more and more of the sport while resistance is gradually increased. And even a professional fighter at the peak of their game does not fight their training partners in training with the intention of beating them, but instead spars at a lower resistance with the intent of improving their abilities and strengthening weaknesses. Rarely is it the case that we actually practice like we play, but instead practice so that we get better at what we play.
This is not to say that a lifter is absolved of their responsibility to practice their sport. A lifter must be able to execute the competition lifts under competition conditions come the day of the competition. However, this does not mean that every lifting session they perform must be a practice session. Some sessions may definitely be dedicated toward practice, whereas others are dedicated to training. As a lifter, it is your responsibility to understand when you are performing one and not the other, and when you NEED to perform one and not the other.