People... It broke! Some parts just fail. Including the expensive a$$ custom shocks available these days. It still happens in this day and age. My '10 Trail w/ KDSS has been running a set of Bilstein B6 4600's since it clocked 32K miles. The drivers side OEM rear shock broke in the exact same manner that this poor fellow's Bilstein did.
It would be worth submitting it to Bilstein's warranty department IMO. Back around 1990 sometime, Bilstein replaced a rear shock on an '88 FJ 62 I used to own because it started weeping oil. BTW - That is the only issue I have ever had with 7 sets of Bilsteins I've put on a variety of vehicles over the years.