Yes,that is exactly what happens. This passenger was returning home to find that United had given up her seat. They later told that passenger that the passenger had cancelled their reservation from a mobile app.
If you are headed home, tired, you do not give up a first class seat on the whim of finding another flight.
Some one at United bumped this passenger to make a seat open for SJLee
That, I’ll bet, is exactly what happened, although not maliciously. I’ll bet SJL got in some gate agents face and bullied him or her. The AI woman drew the short straw..