last night at training we were doing some halfguard techniques (passing, defense..) and later did some sparring from that position. i'm no ground master and the guy i rolled with isn't exactly rickson either. i was in his halfguard, one leg tied inbetween his - i managed to pull my knee out so i got up pretty high on him (but was unable to go to full side control because he still had my leg locked there), so i just grabbed his arm and swung my other leg over his face. so it was really an armbar but my knees weren't together since one of my legs was still entangled in his. i made him tap. so here's my question, is this an actual technique or did i just get it because we're both noobs and he didn't know how to defend? if so, please tell me how such an attack can be prevented so i know what to look out for.