That's a common trope, because people don't read the Open Source Definition. If you read it you'll notice that Open Source and Free Software coincide for all practical purposes. The only instance I saw the FSF and OSI disagree on considering a licence free/open is the Sybase Open Watcom Public License. OSI says it's ok, FSF (and Debian) doesn't.
That is, unless you think OSI is not
the authoritative source on the definition of Open Source and you consider so-called "source available" license to fall in the open source camp.