Isn't this due to being put onto FUP 1 when they implemented the new system...
Yes, user who incorrectly had FUP1 applied on 1 Dec (for 2 hours) got 6 extra priority passes.
Besides the removal of the FUP restrictions, the priority pass removes p2p shaping (while FUP wouldn't have been applied).
For example, if you were in FUP1 and used the priority pass at 18h30, you would have 30 minutes if no p2p shaping, and then 30 minutes of normal uncapped experience, and then 90 minutes of FUP1 enforcement.
We don't know how useful this will be (as p2p seems to be quite good most of the time), but we wanted to give a benefit to customers who don't get in to FUP.