The post numbers are definitely moving slower than the thread numbers. I believe thread 25000 was around post 2.4 million (first two digits were nearly the same), but the thread numbers are significantly into the 3s, while the post numbers aren’t.
There was a similar issue with users where between two specific dates, that I can’t check while I’m not at home June 8, 2011 to September 8, 2013, the user numbers were increasing rapidly (and it showed as such in the now-hidden forum stats).