Scuba instruction follows a carefully planned sequence. Divers start in the shallow end of the pool and do all their skills there. That way, if they panic, they can just stand up, with no harm done. Then they go to the deep end of the pool. By the time they are ready for open water diving, an instructor should be pretty darned sure they are not going to bolt to the surface. It can still happen, but the normal sequence is designed to make it as unlikely as possible.
Skills are done in a similar sequence for similar reasons. Students clear a partially flooded mask in the shallow end of the pool. Then they clear a fully flooded mask in the shallow end of the pool. Then they remove their masks and replace them. In the deep end of the pool, they take their masks off, swim for a while, and then put the mask back on. In the open water dives, they go through that sequence again.
I don't know any more than anyone in this case, but one danger of a non-instructor teaching skills is that they will ignore the sequence and do things in whatever order makes sense to them. This can lead a student to fail at a skill for which he or she is not ready, and if that failure happens in deeper water, it can lead to panic and a risky bolt to the surface.