It is possible that the wheel bearing got hot, which caused the grease to do this to your brake assembly.
When we had our wheel bearing blowout in Phoenix this past January, there was grease everywhere!
Destroyed the spindle and brake assembly.
Both axles and spring sets are being replaced probably next week (depending on when the new axles arrive at the repair shop), and while I'm at it will have all four wheel bearings replaced, even though the one was just replaced in Phoenix, and the other three checked out OK.
All five wheels and tires are being upgraded as well.