Well I just got a call back from the vet and his red blood cell count was nice and high, so he's not anemic (yay!). However, he had elevated liver enzymes (or something like that, she was using a bunch of medical terms). She said this was indicative of him eating a mothball, so at least now we know and I can convince FI this vet trip wasn't in vain.
She's prescribing him some medicines to hopefully bring these down and will check him again in two weeks.
And I hate our neighbors.