This is a pretty ridiculous claim to make from a “cursory search.” Facebook has thousands of patents. I’m sure you searched through them, whittled them down a bit, and skimmed the most relevant-looking claims, but the possibility that one of them reads on something react does is pretty high, and it takes a patent attorney who knows everything about react to say there are no such patents. Keep in mind that Facebook uses this patent license on a lot more than just react; doing this analysis for dozens of open source products would be very expensive. Most companies (and developers) would be best advised to just assume that Facebook has some patent, somewhere, that they can at least argue reads on their open source, or might some day have such a patent. And that would be a problem.