Jeff registered this very forum.
Nah, the forum was kicked off Bitcoin.org in 2011 due to concerns about the lax moderation-- even I was part of that discussion.
In terms of commits: Matt and Luke predated Jeff on the project (by months in Luke's case). Pieter came nine days after him, Wladimir 51 days after that. I was 8 months behind on the commits, though most of what I do has never been coding-- I my logs show that I was the most active person in the development discussion channel the same month as Wladimir's first commit.
Characterizing someone who came later or who was earlier by mere days and less involved as "senior" is a bit of an insult.
Fair enough. I was just trying to expain how the author might have been justified in choosing those words. (I wasn't the author.)