You've already said it all.... "He was quiet, clean, made a list of things he needed to make his stay comfortable, was concerned about the hot water which we couldn't resolve during his visit, and did not interact with us much at all. We would recommend him to a host who enjoys a guest who will provide them with a lot of feedback, requests upfront and will leave a perfectly clean, tip top room looking just like it did when he checked in. We think we we were not the best hosts for XX as we prefer a more social, interactive and laid back guest but think with another host who enjoys structure, he would be a good match. " .... take some of the onus on yourselves since you couldn't really figure out a way to talk to him to make him settle down in a way that made you comfortable and leave it at that. While weird isn't really a reason to give a thumbs down, I think it's appropriate to do that here.
And based on what you've said, I agree with @Kathy101, definitely someone on the Autism spectrum, thus the rigidity, need to try and resolve a "problem" like the hot water, providing you with his schedule of his activities (remember Dustin Hoffman in Rainman - 10 minutes to Judge Wapner) and taking of "his things".