Well, it could be that the cat has unusually small bits. That and a really inexperienced volunteer, and I guess it could happen. When you get him neutered, do make sure the vet checks to make sure the testicles have descended properly--otherwise they could miss one and have to put him under again to get it. (It doesn't often happen, but since the shelter missed your cat's, I'm wondering.) It could just be that they assumed he's neutered because he's declawed.
And what were his previous owners thinking, anyway! They declawed him, but didn't neuter him, so when he wants to fight for females, he'll get ripped up by the other tom! Just plain mean. Not to mention the usual risks of declawing. At least he's got a good home now, poor guy.
In my area, the Humane Society gives low income people vouchers to take to their vets so they can get their animals neutered. My Tiny got his neuter for only $20, though it did cost extra for the rabies shot I got him at the same time.
Before his neuter, Tiny was much more skittish and aggressive than afterwards. During the month after his neuter, Tiny settled down a great deal, relaxed, and became more playful. (He also lost a bit of weight, but only about half a pound, nothing dangerous. He's eating fine now and he's slender but muscular and healthy. Actually, I wouldn't be surprised if he's back to his previous weight by now.) Now, a few months after his neuter, Tiny's really beginning to overcome his history as a stray. For the first time, he's sitting on my lap and purring--though he's still tense while he does it. I imagine he'll be rather a snuggler when he gets to be five or six; but now he's only a year old and still very energetic. You should see the kitty crazies at 3 a.m.... just stay out of the way!