It's just another urban legend, as one of our favorite travel bloggers, Ben, explains at One Mile at a Time.
Years ago we were awarded operational upgrades on United both outbound and return, on a flight to SHA (Shanghai), if memory serves us.
We had volunteered to give up our seats in a potentially oversold situation, and the gate agents moved us into Business Class just before boarding. What a treat, and to have it happen both ways!
The catch is that at the time we were top-tier 1K flyers with UA, so they didn't just pick us out because we were well dressed (spoiler alert - we weren't), or even because we're such nice people.
It's a little like the old joke about the visitor to New York asking directions from a local on how to get to Carnegie Hall. "Practice."