RE: IRS. I'm wondering if it's less that the IRS reached out to Dave as part of an ongoing investigation and more that they're following up with Dave (forgive the incoming nonsense), analogous to how Dave framed the sociologist story.
Dave is a spiteful brat who knows just enough about the law to be irritating (though ultimately ineffective). In another life, I could imagine him as one of those Sovereign Citizen types filming in veterans' hospitals/clinics (not that far off from his atheist activism, attempting to remove religious symbols or implant satanic/secular cemeteries in far-flung veterans' cemeteries) or explaining to bored, irritated state troopers that the United States is a CORPORATION, etc.
If the IRS is actually following up with Dave, I assume it's because Dave reported Dr. Joe for tax evasion, financial abuse, etc. Alternatively, Dave is the one under investigation, and Dr. Joe is necessarily entangled. Or it could all be nonsense, and Dave is just trying to embarrass his father -- Dr. Joe as one of those evil millionaires the IRS is now going after with their new programs.
RE: Ohio State interview. I don't believe the research team cares whether Dave's story is "true." They're looking for "lived experience," the way the estranged party feels, how they perceive the estrangement. I feel for that poor research assistant though, two hours of Dave doing his professional voice and either wanting to play his "receipts" or his guitar....
ETA: Interesting (to me, anyway) that Dave hasn't lately asked for money for food. I honestly wonder what he's doing for money, if Dr. Joe has truly cut him off. No complaints lately about having to eat peanut butter sandwiches on the days he can afford bread.