The BSD + Patents license doesn't imply anything about Facebook's own patents. React may not itself have any patents; that's not the point. The patents involved here are those not owned by Facebook. Facebook doesn't need patents on React to revoke your license to use React if you sue Facebook for patent infringement.
Edit: I see how my reading was wrong. The LICENSE file is still the same old 3-Clause BSD. The PATENTS file is what's new and different.