Different people also I different expectations of senior. I know people a year or two out of bootcamp that have senior engineer titles. Likewise I recently interviewed with Riot games and was told I wasn't a senior engineer and was a good mid level candidate with 10 years game industry experience, and with my title being senior software engineer at time.
Granted the responsibilities of this role sounded more like lead or principal engineer role, but its a good example of senior meaning wildly different things at different companies.
Maybe the person out of boot camp just performed better or were in a role that was better suited? Years of experience is not everything (I wish it were at my age :P)
I tried to word my post to make the point that titles are inconsistent to the point of being random, especially across organizations. Using years of experience as a proxy for seniority always brings up the argument that years of experience and seniority are not the same thing, especially on HN. I agree with this to some extent, but as long as you aren't stagnant as a developer (which might not be entirely your fault) you will gain wisdom that people with less experience lack. That might not make up for a younger persons ability to crunch, or hunger, which could lead to gains in productivity, but I'd argue that people that stagnate later in their career probably weren't great at what they did to begin with.
Granted the responsibilities of this role sounded more like lead or principal engineer role, but its a good example of senior meaning wildly different things at different companies.