Either Chewie just has the worst possible poker face, or the pair may be trying to scam whoever Han is playing by making him think the cards are bad when they’re not.
Since the cards are clearly in Aurebesh, the Star Wars language, it’s difficult to tell at a glance whether they’re good or not.
There’s also a large focus on gambling in the spot, as we see money moving around a table a lot and Han apparently playing poker against somebody.
One of the funniest moments involves Han showing his cards to Chewbacca, and the Wookie being obviously unimpressed.