The MIT license doesn't mention copyright either, except to state who holds the copyright and forbid you from changing that statement.
The actual permission notice says you have the right to use the software without restriction. To me, a layman, it would seem contradictory and unfair if they later claimed that they held previously unmentioned patents that restricted your use of the software.
It might imply a patent license, it might not. I don't think it's ever been tested in court. But at best you're getting a license to the Preact author's patents, if there are any, which there probably aren't. You're definitely not getting a license to Facebook's patents - but because Preact is a clone of React (in outward design, at least), any Facebook patent that applies to React has a decent chance of also applying to Preact. So I'm not sure it helps that much...
Apologies. I didn't notice this was about preact specifically. I agree that switching to preact is unlikely to help with any patent issues. I don't think any free licenses indemnify you from third-party patent claims.
The actual permission notice says you have the right to use the software without restriction. To me, a layman, it would seem contradictory and unfair if they later claimed that they held previously unmentioned patents that restricted your use of the software.