Note that this is only average base salary, not total comp. I imagine that this skews low when looking at public tech companies that pay out significant amounts of total comp in stock grants and bonuses. Not unusual to get 50% or more of total comp as non-salary.
On a sidenote, there seems to be a dearth of positions for junior devs in Seattle as of late, though lots of roles available for those with 2 to 10 years of experience.