Interesting scenario.

The only instances I have heard about are on NW, where Platinum Elites get a 1,000 RDM bonus if they aren't upgraded on a domestic flight with a FC cabin. Although the NW website is vague about this, FTers have reported that you get the bonus even if you are offered the UG and decline. I have heard about this happening on short hops.

That said, even most NW PEs would probably take the UG for a long overnight flght like in your example.

Maybe he just didn't like the looks of his prospective seatmate?