I choose to believe it is Abner, he's kind of the Ben Kenobi figure to Indy and was a heavy influence on him.
He's so different from his father that Abner becomes his father figure and where Indy learns all his tricks. Stuff like the gear and so forth could have come from Abner too. It's a cool little story element if you think about it.
It's like Mutt, i thought Mutt should have been more like Connery, leaving Indy to be the outcast lol.