Jon Anderson's version of events never seems to reconcile with the general consensus of anyone or everyone else, and add a few decades of time in between then and now, and he basically has no idea what he's talking about. Okay, he knows what he's talking about, but it usually has nothing to do with reality.
The Union album is generally considered a Frankenstein creation of Jon Anderson and Jonathan Elias. As has been pointed out, it was mostly made up of tracks that ABWH were working on for a possible second album, and some songs by the Rabin-led 90125 lineup. One story I read said that Jon had asked Trevor for a song, thinking that they needed something more accessible (more "pop") for the new ABWH album and Rabin sent him three, expecting Anderson to pick one. Anderson said Wow thanks and took all three. Eventually the 90125 lineup, and a new solo acoustic piece by Steve Howe, rounded out the album and they repackaged it as a new Yes album.
But that was all still basic tracks, and when it was time for edits and overdubs and other fine-tuning, Bruford, Wakeman, and Howe were already done. They weren't that invested in ABWH if it was just going to be another version of Yes, and now that it was offically Yes, they found more interesting things to do. So Anderson and Elias hired a boatload of session guys to do the overdubs. Wakeman always calls this one "Onion". My first thought was because of all the layers (like ogres have layers) but it's because it always makes him cry. He says he listened to the album once, couldn't even hear anything that he'd actually played, and through the CD out the car window. Howe has made similar statements, and I don't think Bruford cares enough to even comment. It was just a paycheck for him.