I'd say that's overstating the case. You aren't granting them a license to your patents and you can still sue them for infringing (which you would not be able to do if you granted them a license).
Rather, you are promising to look the other way for as long as you are using React. Should you choose to sue,
1. You can say in your case that they never had a right to your patents
2. You can take the time to remove your usage of React prior to filing the court case (so that you never infringe).