I've never heard anyone say "the corporate". Usually they say "inventory" (or whatever department did the deed). How odd.

Looking at the flight, it seems to be packed to the gills. It wouldn't surprise me that someone has concluded that someone who booked in F is not going to go in F, and decided that someone should be someone who paid in miles, not dollars.

Here's what I would do.

(1) Ask to be put on the waitlist for First. There's always a chance of a no-show, and since the ticket is paid for, your friend should be close to the top of that waiting list.

(2) If forced to go into C having paid for F, I would think having at least 15,000 miles refunded would be in order. That's the difference between a Standard F award and a Standard C award, one way.

(3) Normally I would be inclined not to give up my seat on 838, at least until I got to SFO. A lot can happen between now and then - the waitlist might clear. Flights could be early. Flights could be delayed. They might - or might not - be offering additional compensation for a later flight.

Looking at loads shows UA872 has no seats for sale in F or C. UA838 (2 hours later), which is 3 class, has a few seats in F, none in C. UA220 (5 hours later) has seats in F, but is 2 class. So it's possible that if your friend doesn't grab the F seat on 838 now, he'll never get it. So there is an element of risk in the "wait and see" strategy. But I'd probably still go that route: at SFO my options would be clearer.