It’s one of those little differences between the English and the Americans, the way in which those from the east side of the Atlantic often make gentle self-mocking references. It pops up all over the place, where an American who won an award might say they were thrilled, honoured, delighted, the old style English response might be a light chuckle and a “Don’t know why they picked me really, I’m not unusual”. One can take these sterotypes too far of course, we have our share of self-aggrandising egomaniacs just as they do (Trump and Jeffrey Archer anyone?).
Anyway, here’s a quote from GW Bush, talking about Arnie the Terminator:

“We share a lot in common,” the president announced, in self-deprecating style to a Santa Monica audience. “We both married above ourselves. We both have trouble with the English language. We both have big biceps. Well, two out of three ain’t bad.”

I do wonder sometimes about the visceral hatred of GW that so many in the UK seem to show. At times he sounds like one of us.