Sam is not one to take someone's word on things.

Based on the way he's talked about this, I think he has been shown data or materials that make it clear that something 'spooky' (in his words) is here.

Contrast that with Neil deGrasse Tyson who has been downright hostile in recent months, probably because he and others spent decades speculating about microbes on Saturn's moons instead of taking ufos seriously.