Well, the React PATENTS file seems to indicate that you would lose the patent grant for any patent assertion against Facebook,[1] not just for software patent assertions against Facebook. So, it's theoretically possible that the poster in the parent comment was concerned about a patent on something other than software. Maybe he or she has patented some type of VR headset, for example, and uses React VR for the software that drives it. He or she might reasonably worry that suing Facebook for infringement on the VR headset would result in the loss of patent protections concerning the React VR software.

[1] The language I'm thinking of is the part that says that the license terminates if you initiate "any Patent Assertion: (i) against Facebook or any of its subsidiaries or corporate affiliates, (ii) . . . "

I agree that it is a legitimate concern if you believe that only software patents are a problem but want to keep your other patents available.

They probably left it this way because there is no legal definition of a "software patent" - they cannot differentiate between those and "other patents". It's not like "other patents" are all sunshine and rainbows either - the patent system is fundamentally broken.

IANAL, etc. This is indeed a very problematic bit. I'm not sure if it is even possible to restate that patent grant in such a way that the termination clause would apply only to software patent assertions and simultaneously keep the text sufficiently unambiguous.