I was able to repro on my localhost
A couple days ago I created ScrollGuy1.
After the account was approved he visited but did not read any topics.
The next day, he went to the 100 post challenge topic.
Being a new member, it opened at the first post.
He did not read any posts, but used the progress slider to jump the the last post, and then promptly left.
Waiting until today to give sidekiq a chance to run jobs, I went to the Users page and ScrollGuy1’s Profile.
It seems the Profile post count is when “the blue (read-state) dot goes away” and the Users post count is using “highest post number seen minus lowest previously unseen post number seen”