Yes, but it also affects you in the case that you argue that some other, unrelated Facebook patent is invalid, even if you're happy to concede that the patents covering React Native are valid.
For Google's use case, it means that if they ever find themselves in court claiming to have prior art on any of Facebook's patents (let's say Facebook sues them over something G+ does, and Google says it was described in the literature well before either of them), they automatically lose the (patent) rights to all of Facebook's OSS, even if they're legally in the right. So they can't build anything they care about on React.
If that reading is correct, you can still use React Native to the extent that doing so doesn't violate any of Facebook's patents. They could argue it does and you could argue it doesn't. Until and unless a judge ruled that it did, you could continue using the software.
Edit: Geofft that's a good point. I suppose this really is a poison pill for a sufficiently large company.