It may or may not be considered misleading in some countries, but it's pretty standard practice in America.
I'm guessing it had an asterisk on the advertisement, saying in small print below "with purchase of 2,000 credits."
In fact, here is the advertisement that I got in my email:
Free Legend Golf Balls for Ryder Cup Weekend
Buy $20 in WGT Credits and get 3 free WGT Legend GI-SD2 virtual golf balls
* One time offer for Legend players only for purchases of $20 or more WGT Credits thru Monday, October 4th.