Would someone please tell me how this is offensive?

So i work in a world wide mechanic shop, and had our christmas party last night. Anyways me and one of the mechanics are pretty friendly, we joke around and whatnot, however i'm 21 and he's probably 60 something, but were both play music so we get along. Anyways he brought his guitar and asked me to play something, and he always talks about how he's fullblood spanish, so i said "okay heres a spaniard song for you" and started playing a clical spanish song and he got pissed calling me a racist? everyone in the room was socialising and it was just me him and another guy sitting down so it's not like i called him out in front of 30 people. I don't have a tolerance for people being overly sensitive so i told him to stop f*****g crying, and we haven't talked since. I really don't understand how this is offensive considering he's always talking about his heritage and what not.