Beeg--
He's doing a recovery job. I'm going to assume for the moment that Hunter is a complete moron and has no encrypted files, even though a lot of this stuff should probably be, and would be.
So, in the course of recovering the files, he saw something that was criminal enough to have friends call the FBI. Then, the FBI shows up unannounced, takes the computer, and does nothing as far as anybody knows.
He also gives a copy to Rudy, because somehow, he knows how to get ahold of Rudy, and passing along a customer's data to Rudy seems like the right thing to do.
Oh, and keep a copy for yourself too, because Seth Rich.
He thinks it was Hunter who dropped it off, but despite being able to see photos of Hunter smoking crack, he can't say it was Hunter. The person who dropped off three computers full of crack videos doesn't return, because, well, not that big a deal. And somehow, it's easier to call Rudy, than Hunter, who probably could be reached pretty easily through the Biden foundation, or the Biden campaign, or all kinds of things with phone numbers on the internet.