I don't see that claim being made in any way. Encrypting data at rest and data in transit are two very different things.
If Syncthing encrypted your data at rest, you would not be able to access your files! (This can be a good thing in a limited number of scenarios, but not in the majority of cases). Someone can gain access to your computer and read your files whether or not Syncthing is installed: Syncthing never claims that it will make your computer more secure.
The thing that Syncthing adds is the ability to transfer your files. Therefore encrypting data in transfer is important. This is what the claim relates to.
HTTPS encrypts your data in transit: if it encrypted it at rest, you would not be able to read the webpages you were browsing. That does not make all claims about HTTPS being secure "misleading".
I don't see any attempt there to claim (or anywhere else) that Syncthing encrypts your files on your computer. That statement is explicitly about communication, which is why it says "communication".
How else would you word it?