There are some things you can rely on. Any sort of trusted advisor to royalty is likely to be an Evil Chancellor of some sort. And a goatee in this situation is pretty much the kiss of death. So Qui-Gon's reaction here is perfectly understandable survival instinct.

Transcript

Obi-Wan: Queen Amidala, I presume.
Sio Bibble: You must be the Jedi ambassadors.
Qui-Gon: Who are you?
Sio Bibble: I'm Governor Sio Bibble, the Queen's trusted advisor.
Qui-Gon: Advisor? Hmmm. Does he have a goatee?
GM: Yes, actually, he does.
Qui-Gon: We keep an eye on him.
Obi-Wan: Seriously, if you need help coming up with names, I think Sally's got that covered.
Sio Bibble: We need to get to safety.
Qui-Gon: We follow Bubble... cautiously. Expecting a doublecross.
Panaka: Get their weapons.
Qui-Gon: Hey! We killed them! Get your own loot!