It's always weird gymdads who walk up to you and tell you "you're doing this completely wrong, stop doing it" but never tell you why. I'm convinced a lot of them don't even really know what is right or wrong, they just get an ego boost saying that. Like, cool, thanks for letting me know I'm doing it wrong, but, y'know, since you know the right way to do it, shouldn't you at least tell me what is wrong instead of just saying it is wrong?
That's why I was motivated to learn the proper way to do stuff, so that even if they come to me again, I can just explain them why they are wrong instead.
Whoah, guess it worked.
I've had a guy come and explain to me that I'm breathing wrong because I was exhaling when lifting and inhaling when lowering when it doesn't even matter what you do when you're doing normal lifting as long as you're comfortable and to top it off I was actually breathing the way that he was instructing me to breathe.
How was he instructing you to breathe? Generally you actually want to not breath through the movement, but instead do the Valsalva maneuver and only breathe at the shrot pause between reps. It's true though that for very light weight it doesn't matter a lot, but generally you want to do the VM to better stabilise your spine.
I was using the VM which confused him so he told me that I had swapped inhaling and exhaling because my inhales and exhales were pretty much identical grunts.