Not a fan of FB here. That comment is nonsense. It is completely unthinkable that Facebook would do this.
Facebook is a (among many other things) a software company, and software companies do warfare with patents. It might be their least favorite weapon, one they have yet to use - but "unthinkable" can only refer to your beliefs -- it is actually extremely thinkable, even if at this point in time improbable.
I'm really concerned about zstd working its way into some future de-facto standard file format, though - I think the name "zstd" is marketing genius (of the evil kind).
(1) can afford to roll your own framework
(2) can afford the lawyers required to point out that this doesn't hold water