It is possible that it was not your son that made the call. My parents had a call purported to be from my nephew asking for money to be wired because he had been arrested because he was with some friends who had drugs. It was a complete fabrication by some scammers. My nephew has never been involved in drugs and was not in the location that the caller said he was.
If you do a search on "grandparent scams for money" you will find a number of links to news reports of such scams.