What a tragedy 😢
With hindsight there were a couple of red flags here.
Firstly that the main person at the charity was unaware of the background of the kitten - all animals that they take in should have a record with details like background (pet, feral, stray), where they came from (e.g. handed in by owner, found on streets, part of a colony), approximate age, condition on arrival and a running record of changes etc.
Second red flag was that the paperwork for the adoption wasn't to hand when you picked him up. With mine, my DSis's and my DSil's rescues cats in all cases we received the paperwork on collection including a full background & history of the cat(s), vet records with inoculations, any current conditions (e.g. one had luxated patellas), and in the case of mine a list of their preferred foods, treats, even toys. All this handed over to be looked over and read before the adoption papers were signed & the cat handed over.
It does make you wonder about some rescues and fosterers though. The 2 independent rescues I've had anything to do with are both excellent in this way - one doesn't foster at all, the other are incredibly fussy about the people who foster their animals and regularly check on them.
But I've heard about rescues who are so desperate for fosters that they don't vet them properly, and also where decent rescues have had to take in the entire population of bad "rescues". There are also some well meaning independent rescues who are OK with the animal side of things, but when it comes to the more "business" side of things e.g. record keeping, can be hopeless.
OP I do hope you find a nice, healthy kitten (or two preferably) soon. I would suggest that you don't try to follow up on what happened with the first one, as if you hear nothing you can tell yourself he recovered.