I think O'Connor is trying to get them to habitually do the right thing. That can be a long process with younger players and can get ugly at times. I'd rather that they win playing the right hurling, than just win. Winning ugly is a habit and this'll stand to them. They can, and will, get better.
He's definitely put a bit of fire and fight into them - which was welcome. Clare were winning a hurling match. Their manager turned it into a war, and Cork came out on top. We used to lose the wars, but the old blood and bandage fire is back under O'Connor. With or without an extra man, a 13 point turnaround is seriously impressive at underage level.
The sending off didn't look justified. But the linesman was pretty clear he saw something, so I wouldn't presume to know better based on a bad camera angle. One of the Clare players was immediately in the Cork lad's ear too, which seems to imply he knew that his buddy was in trouble. Either way, if you're Clare, you have to be asking why a player gets involved in something like that, just after a row. Best time to get an early shower for yourself.