That was part of a freeroll series put on by the affiliate known as RTR. I use RTR a lot, they're very awesome. They have a lot of promos where new players to a site can earn entry into $5k+ freerolls
for raking $1 in their first month. Existing players qualify with $50-100 rake, depending on the site. Generally quite small fields in them too. I do one monthly on a Merge skin ($50 rake per month) for a 5k freeroll that usually gets around 60-80 players. Sick value.
PM me if you'd like details/hookup/etcetc