Interesting. Flying out of SFO, I’ve seen it several times over the past few years, also logging a good dozen overseas flights per year ...

I've seen that as a TSA thing, on a domestic flight. It was on the first flight in the morning, so the airline wasn't trying to do a quick turnaround.

It also only covered the people standing in line... so I sat there, waited for my boarding group to go, and followed behind them.

yep, i've been pulled aside on the jetway while boarding a british airways flight to the usa, to have my carry-on searched. this was in heathrow, so not sure who the particular security agent worked for. none of my phones or electronics were turned on or checked, though...