Thanks for all the great responses!
His stomach isn't hard, it is pokeable, but it's not super-squishy. His coat is also soft and fuzzy, not coarse at all. The vet hasn't gone the FIP route, however I was told that he is on the thin side. ~2.1 pounds at approximately 10-12 weeks of age. He has gained some weight since we got him last week, which I suppose is a good sign.
We have heard gurgles a few times, and he's been gassy a few times, his poop as I mentioned, has been on the soft side since he got here. I'm not completely sure what it's supposed to look like, but I was told that it shouldn't be soft. It was "cow pie", but now it's soft, but "formed".
Also, it seems that they originally weren't sure if he was a male or female, they shaved him for both spaying and neutering, and I guess determined that he was a male after doing so. Maybe due to underdevelopment? Not sure. He is very excited and playful, hasn't shown any negative signs, or what would appear to be sickness. A friendly little guy, emphasis on little.
I'll ask the vet next week if he should be de-wormed again. I'm currently giving him anti-diarrhea medicine and his stool sample came back negative for parasites/worms.
Thanks for the replies, here are some more photos:
He just started going nuts and clawing at everything, running around bonkers. Time to ignore him a bit... photos made him go nuts apparently.