Was he pissed because I was better than him in snowboarding?

Well it is common for guys to try impress a girl with what they are good at (as the age-old courting ritual goes), so if you were better at him at snowboarding he may feel at a loss of ways to impress you.

Was he aggravated on the slopes? If not, then I wouldn't think so. If he seemed like he was getting annoyed then yeah maybe. I'd only be mad if I had been snowboarding for years, and you just picked one up and were better than me. I'd be more mad at myself then you though. The same for everybody I think. If you had been snowboarding for years and some kid who just started was out-doing you, wouldn't you be mad? If you both were just starting, and you were better I wouldn't be mad either. If you both were experienced, and you were better, I may be mad, but probably more at my own performance.