Those are good questions for the ages but not the point of T's post. His point is quite simple. While he has been working to grow membership and finally reached 25,000 members over a period of years (and that is after eliminating more than 3,000 inactive members over the same time period) he takes a look around and sees another forum advertising substantially more members and doesn't believe it. A quick look and he sees what he saw. I must confess I got curious and tried it and yeah there are several thousand less than advertised there.
Now in reality many forums do this. Heck you can add a specific plug-in to randomly add members. That is not the way T runs this site. Everyone can do whatever they want.