Few things about this, based on what I've gathered on it:
1) Doctors/medics will always heavily recommend you go to the hospital as soon as an injury occurs. Even if it's minor and they don't actually think it needs further medical treatment. If you're under their watch, and something happens, and they don't send you to a hospital, and then something transpires that causes the injury to become worse in the absence of a hospital visit, they're in big trouble. They really need to push to make sure you're 100% aware so if you decline further attention, they have less fear of being held liable should things go sour. So the break was likely not even that bad - if it were that bad, at his age, he absolutely would not have been able to perform, no matter how much of a "rock star" moment it would've been.
2) Of course he didn't take pain meds. Has anyone here ever been on pain meds? No way would he have been able to perform if he'd taken them. However, alcohol, obviously, that not only helps, but adds to the "rock star" persona. He likely wasn't in that much pain, but obviously standing on it would've been stupid, and overall this was just a really good excuse to get drunk. If he got too drunk and his performance started to waiver (which it might've, I haven't seen any of it), well, he's got the out of "Of course I was hammered, I broke my fucking leg!"
3) It must be depressing being the medic holding his cast. Sure, he's getting paid well, but now the rest of his life, all his peers are going to know him as the guy that held the cast on Dave Grohl's leg in front of a sold-out stadium. That isn't a very good claim to fame. It's actually pretty humiliating. Maybe if he was the guy that saved David Grohl after a fan shot him a few times, but this? Nope. Just embarrassing.
I'm expecting to get piled with downvotes because of reddit's blind love for Grohl, but there are realities behind what happened. I guess when your main audience is teenagers and college kids, it's incredibly easy to pull over their eyes and look like a God over explicable, incredibly underwhelming shit.