Hilton HHonors - Unknown Promo Points

I stayed at the Pointe Tapatio last weekend. I received 500 points for Hilton Brand Promo, another 500 points for Hilton Brand Promo and 500 points for something labeled AMEX COBRAND BKG BNS. Anyone have any idea what these are and why I received them - not that I'm protesting, but I'd like to know what I need to do the next time to get them again.

The AMEX Bonus is a promo that began April 15, and is due to Hilton launching its AMEX cobranded card. If you book a stay and guarantee it with AMEX, you get 500 points bonus. You are supposed to have a Hilton AMEX, but it appears that use of any AMEX triggers the bonus.