BBC

I think it was just shrapnel from the teleprompter and he was playing it up to milk it... as he does.

The best explanation I've heard is the shockwave from the bullet split the skin on his ear. Think of a papercut that bleeds enthusiastically. The cute itself is fine enough, and the area has generous blood flow, so it heals rather quickly. But it looks worse than it is when it happens

He got nicked by something, probably a piece of debris, maybe from a shattering teleprompter?

Lots of blood vessels there, a little nick is going to bleed a lot, and still heal relatively quickly.