I'm trying to understand what the real world implications of this notorious clause could be - obviously a lot of it comes down to legal interpretation but would

I'm trying to understand what the real world implications of this notorious clause could be - obviously a lot of it comes down to legal interpretation but would be interesting to know people's thoughts. Say my company patent some key part of a product, and Facebook then release a product which infringes on this patent. If my company were to sue Facebook for this (unrelated to React) patent infringement, then as I understand it, this patent clause would cease to apply to my company. Does that then mean that Facebook could countersue my company for using React, saying that some part of React is patented and my use of it is therefore infringing that patent? This seems kind of weird to me, as React is a product that they put out there for people to use - it's like Microsoft suing me because I use Office and they have a patent on the ribbon UI or something. Or does it just mean that some third party could claim that React infringes on some patent of theirs, and they can then sue my company saying my use of React infringes on their patent? (Whereas previously Facebook would protect my company against this) Or does it mean something else entirely?!