I do see Griffon in the pugnacious expression and domed skull...given the relative popularity due to that movie...I'd buy someone mixing it into Yorkie or Cairn for certain. It's the "in" thing to do now.
I'd say he does look a bit like a Brussles--here are some pics of my Honey gal for comparison:
Obviously your little guy has a snout though--which good Brussels do not (some poorly breed do though)--maybe mixed with yorkie?
Just a note that Brussels are a double coating breed that if you want a nice coat you need to hand strip (which means pretty much pinching clumps of hair for hours)