"I didn't Look At My Cards. All-In." - Did I Get Angled?

Weird hand in a splashy 1/2 game last night. Nevada casino.

Before the hand, Button slides out $50. There are button straddles allowed in this game, but usually to $5. Dealer clarifies that this is a blind bet.

Folds to UTG+1 who goes all-in for $300 and claims that he didn't look at his cards. Everyone folds (including Button) to me in the BB with A6o. I cover.

I say "You really didn't look at your cards?"

He insists that he still hasn't looked. I'm not sure that I believe him and I'm leaning toward folding, but then the dealer says "He didn't look."

Result:

!I call. He turns over AQs and holds.

What would you do in this situation?