I think you got your "Silver" and "Business Class" mixed up
bora...must have been inbibing too much of the J Class wine
Operational upgrades (op up's) are a mystery to most apart from Yield Management. Being Silver, you might have merely been lucky - in the right place at the right time. As you don't mention where the op up happened (ie. at check-in, Lounge or boarding), perhaps all the other CL's, Platinums an Golds had already checked in/boarded and they were looking for additional status members to bump - so count your lucky :-:'s