At first, I thought I might had been doing something wrong so I kind of went with it as I've never had anyone critic my form before, and then after about two more sets from when he first mentioned something, he showed me what he thought to be "correct" form on the smith machine since it was literally right behind us, and thats was when I had my "oh shit, this guy doesn't actually know what he's talking about" moment. Lesson learned though.