I suspect the culprit here is plainly visible in the distorted face that's been photoshopped on to the picture hehe.
Someone saw Spike, thought his pic was really hot, put their own face on to it, and probably started sending that out to unsuspecting hookups in gay chatrooms online or anyone else he wanted to impress with a body and penis that wasn't his own.
And then the photo eventually found its way to DudesOffCampus as a user submission.
Apart from someone having at some point along the line snagged one of HornyBritishBoys' photos (Spike's a hottie, btw), I think it's more funny than anything else hehe.
Cuz I can totally picture someone taking the pic and throwing their face on to it thinking "ohhh man! this is gonna get me soooo laid!"