Yeah, two unlikely events had to happen here.

First, two PFRs and a button caller had to check this flop.
Second, someone had to suck-out on your set.

Luck in poker is a deeper, more complicated beast them just card frequencies.

c/r vs b/r really comes down to how these guys are playing and/or what their body language was after the flop. Without being there, it's hard to say.