I realize a million is a bit unrealistic, but if you're going to make a public statement, at least back it up or prove to the guy why his findings don't constitute a "million-dollar bug". It's not right to just cold-shoulder the guy and hide behind vague rules that were never clearly outlined. In fact, you might even conclude Facebook brought his behavior on themselves by making such a statement as "if a million-dollar bug is found, we'll pay it out." $2500 is nothing when you're thinking $1,000,000