That tweet was mildly petulant agree but not particularly outrageous "what doesn't kill you makes you stronger" is a pretty well known phrase after all - the public smackdown by Emery was incredibly OTT in my opinion. If that raised Emery's ire he'd have had a field day with Kev storming off the subs bench, media moaning and throwing his gloves around let along half the hi-jinx a lot of players get up to!
And other than that one mild tweet what is your evidence for a young player behaving badly which I generally class along the lines of partying, throwing huge strops, fighting, showing up late for training, being rude to fans etc?
If I read it right ESPN have Kolodziejczack as 18, he's actually 24 so whilst technically meets the criteria think it a bit of a stretch to call him a youth player.
https://en.m.wikipedia.org/wiki/Timothée_Kolodziejczak
Perhaps Sevilla don't have a good academy setup, I honestly don't know, and he might be excellent in other ways but on the evidence I've seen so far he doesn't seem to have the particular focus on youngsters I'd prefer in our next manager.