My dad was a very insecure person, kind of dependent, and he indeed had a very authoritarian and judgemental mother. So, in the end, even when I was the one who face to him more when a kid, I was the one who better understood him when I grew up and did therapy for my issues. Because I was very alike him.
He had a very nice bottom after all. But, he surely was trying his best by repeating his own triangle roles patterns.

You did it so well when facing to the situation your child lived with this trainer. He did the worst an adult could do, to pay their insecurities on children by controlling and making them feel scared. It happens a lot, more often than we want to believe with adults who deny themselves to grown up. He’s a very dark person. Hope, he learns to be better.

I would like to thank you for your support and your insight. Like you, one of my main goals is to understand the why and what’s behind these behaviours. So, yes, I also wonder why I feel triggered and at the same time, also wonder about what’s behind a person’s behaviour. Because in the end, none of the behaviours are strange to us.
In my introduction to this thread I confessed that I felt triggered and I behaved very bad with a user here ( I mean, I pissed her off on purpose). So, I’m very grateful for the replies here and what I have learnt.