I thought Poker was a game of understanding your opponents not only based on past actions with cards but also by looking at facial expressions, body language and determining whether or not they have a good hand. Along with that, a big part is developing subtle gestures to throw your opponents off.
Without this information, isn't this win somewhat random or "lucky" and not really indicative of how the AI can play against other humans?
Nope. The game is pure statistics based on the known cards, which computers are very good at. Collecting a database on your opponent's habits is also far more useful than looking at their face could ever be. After all, their body language is only an inevitably misleading stay stream of data, controlled entirely by your opponent, whose entire purpose is to throw you off. You're much better off completely ignoring that distraction.
Also, what better "poker face" is there than an emotionless calculating machine that you know will always make the mathematically optimal choice? That has to be unnerving to play against.