Hi, that's a tough one! Did you advertise the fact that you had found a male kitten? If he had only been missing from them for a day, why was he in such bad condition? Have they given a good description of him to you? For example, my cat is jet black, but she has a tiny white patch on her belly that would make her identifiable to me. Mind you she is also chipped, tagged, wormed and frontlined!!! If you decide to let them take him I think a little chat on pet care might be in order. I understand that kittens, puppies etc can escape, but......
Good luck
Lisa x