I never heard of such abuse in a swimming instructor, and I have been around a lot longer than you.
@DandyDon & Marie13:
Abuse? Yes. Uncommon? No. Depends where and when. In my case I am around a bit longer than Marie13 and likely less than DandyDon. Grew up in a small town in southern Germany, maybe 7500 inhabitants in town not counting surrounding villages. Weirdly enough it had an Olympic size outdoor swimming pool with a fun shallow bay off to the side of one end and a deep dive board bay off to the side on the other end. The deep end. (Well, maybe 10 feet and a bit).
It also had a very active swimming club and a very active head of that club (and in charge of the pool). That little sleepy town had at that time (60s 70s...) regularly competitors at state championships.
Every kid going to grade school could at least swim and by grade 3 or so most swam impressively well. Some not, but they swam.
Some kids got exited about jumping off the diving boards we very little and survived by adopting an instinctive dog paddle or by firing fished out. Some did not dare.
Almost every kid not figuring out a doggy padfle of sorts, whose parents (nobody has heard of baby swimming in that town in the 60s yet) wanted for the kid to know how to swim by age 4 or 5 (before school, because swimming was a thing and water was a thing and once you swim you are safer...) learned to swim by this exact scientific method:
"THE" swimmaster either was approached by the parents or convinced the parents that it was "time". Then the by deep end scared lingering kid was approached by "THE MASTER" (I kid you not, a person commanding absolute respect (well, from little kids, he heard about it later) and a talk about maybe starting to learn to swim was initiated. At an unsuspecting moment "THE MASTER" grabbed one wrist with one hand and an ankle with the other. A one and a half turn Olympic hammer throw moment later the little person found him/herself catapulted to about (so it seemed) "THE MIDDLE OF THE DEEP END".
Most came out with one or another improvised style of doggy paddle. Crying and screaming. Mad as hell. He had a way of getting you with instant gratification so.
He just looked at you and asked what happened. You complained your little heart out about the horrible deed. He just went "And then what happened, how come you're here, what did you do?"
A very big light bulb went on instantaneously. And he had another customer for the club to learn this new thin, swimming even better...
That was the easy part.
But some had to be fished out. And we're traumatised. That was the hard part. To his credit, that (expletive) lost no one and stuck with working the (very few) traumatised ones more tenderly until they swam and had their light bulb go off.
I was one of those that got the instant lightbulb, my sister went down like a rock and little as she was almost killed the guy in anger....but she swam like a champ too, because she got convinced that there obviously was in issue that needs working on...
Different times, different place, different methods. Where it did not work was older kids, or kids that moved to town later in live. They just had to learn the hard way, slow and methodically. Well, I am saying that, I did not throw my kids in the deep end... but I made sure they swam...
That swim master. I mean "THE SWIM MASTER" definitely was a bit rough around the edges and definitely would be out of place these days. But he did know what he was doing. Definitely had a way of making a kids mind go "Oooohhh" ... ... one way or another... and he followed up and left no one behind... Was one of the head judges for swimming events at the Olympics in Munich too and don't know what else... But he sure is not from this time...
Morals to this story?
None. Just sharing the story.
Well, maybe one thought: If you are going to do that sort of abusive thing (I am not saying anyone should do this, I am not saying it's right), what's worse than doing it is to not follow up to the point where every kid actually does swim and no "traumatized roadkill" is left behind.
Sorry Marie that you were the victim of a copycat imposter of sorts and we're left to deal with your "Trauma" on your own.
All that said:
I am still at a loss as to how to have my wife find a way that works for her to get really comfortable in the water. No, she is not from that town or country...