I think it's a red flag when it's also attached to a certain kind of confidence that their bootcamp experience was on-par with years of experience or education. As in, the kind of attitude where that they feel that because they went through the exhausting bootcamp stage, everything next is just an application of what came from the bootcamp. It's something I've only seen with programmers from bootcamps.
Honestly, never encountered that. In my experience bootcampers are usually self-conscious about their background. Maybe they behave differently at small companies/startups (my experience is at a big tech co)?
That could be it. I work outside of "tech" these days at smaller orgs that naturally attract people with significantly different personal motivations to those in the tech world.