These are college-student or occasionally grad-school programmers who qualified to enter the ICPC World Finals, generally by performing sufficiently well at a regional championship to qualify. You can read actual rules here (see "Advancing to the ICPC World Finals"):

https://icpc.global/regionals/rules

I don't know what you mean by "elite", and there are certainly plenty of teams at the World Finals that are not especially competitive, and there certainly many elite programers who don't qualify for various reasons (most obviously by being the wrong age or not in the right stage of school or having already attended too many times), but I find it hard to believe that there aren't enough "elite" programmers present to make the winning teams be genuinely elite.

Compare to, say, the Olympics or pretty much any academic olympiad. There are many people and teams at the Olympics who are not remotely competitive with the winners.