I was running through the wasteland when I came up with a group of random guys that were beign confronted bt some other guys in power armor.

The guys in power armor said something and then wasted the guys, then they turned to me and said "this is not your bussines" and walked away.

I though they might have been Enclave but one of the guys was freaking huge, like a super mutant.

Any Idea who they are?

The huge guy is Frank Horrigan*, the other ones are Enclave troopers.

* = SPOILERS ! ! !

Actually it's not random. Every player gets to see this scene. You'll meet this guy much later in the game.