Hmm, do you know which spot in the video they discuss that (it's a long video)?
Seeing that they are using just controller cards instead of raid cards, and FreeBSD, it seems even if they were not using specific features of ZFS, the performance and other automatic things ZFS does to provide superior (compared to most (all?) other filesystems) data integrity and protection... they would be using it by default...
It looks like they are heavily redundant boxes with the goal of reducing field maintenance, running FreeBSD as the OS.