Double check with Salehoo to see if he is still an active member firstly, then you may be able to make contact with him here again.
My opinion would be that he wanted to use someone else's account, other than one of his own for a very good reason.....and now you have the bill for that reason!
Have to say that you may have been trying to be helpful, but don't trust everyone because they are on the Salehoo forum. No doubt the vast majority of members here are genuine, but it's also a good fishing ground for the odd scammer.
Not Salehoo's fault, they build a great site, but it's only natural some scammers are going to pay a few dollars to join if they think they can id some easy marks.
Who knows, you still seem to think this member is genuine for some reason, but if it walks like a duck, squaks like a duck....well!!