The titles are arbitrary and mostly a pain in the arse.
The designers of the software created extraordinarily stupid titles to represent how many posts a user has. For example 0 thru 10 posts is an something, 11 thru 25 is something else, etc.
Whenever the software gets updated, the software resets everything so I decided to turn the feature off for the most part.
The "Vegas Rock Star" thing is a way of paying special homage to the people that went to the meet 'n greet in Las Vegas and everyting else is something random more or less.