Or... maybe he just needed some traffic to his website.
It seems everyone who had anything remotely to do with Facebook's origins has tried to cash in.
This bothers wantrapreneurs because it highlights just how much luck plays a role in a story like Facebook's. They want to believe that one founder or a few co-founders succeed based on some factor(s) under their control (hardwork, skill, etc.)
Greenspan is just another one of those people who was involved and is trying to cash in.
If anyone needs to "get over it", it's people who just can't accept that huge fads like Facebook are unpredictable and uncontrollable, and that when faced with the possibility of huge sums of "money for nothing" it brings out the worst in people all seeking a share of the bounty.
The web is a lottery.
Time to re-read the recent speech from Princeton's graduation ceremony by the author of Liar's Poker.