Is it at all possible someone could have hurt him in a particular way, and he is reacting whenever someone is doing the same sort of mannerism which might have hurt him? It might not be the same person but could be mannerisms and scents?
I've also heard of chins being jealous of other people sometimes around their owners. I admit, my husband had one chinchilla years ago, that he basically raised from when she was only 2 days old... She didn't like me or anyone else. Wouldn't come to us, didn't like us (my mother and myself) holding her (she'd make grunts and kick with her feet.).
Yet she'd run to him if he tapped his fingers on the floor, or held his hand out for her to hop on. She would sit on his shoulders for hours at a time, watching whatever he was doing. But if I came over, she was not particularly friendly to me or to anyone else. I got the feeling she was jealous of any interaction anyone else had with him.
I love chinchillas more than anything and never laid one finger on her in any sort of mean way, but just seemed to be some sort of weird jealousy or something going on/possessiveness maybe?
I've heard very rarely, but a few times with other pet owners, of chins attacking their spouses legs when their spouse would sit with them, or attacking/spraying others (females generally) that weren't their owners. It's not common but I've heard of it a few times.