Modanung It is true that free/libre requires access to the code, which I believe some would call "open" in a sense, and a lot of the freedoms of open source and free software are basically the same. Naturally, this is because the Open Source Definition is derived from the Debian Free Software Guidelines, which operates based on the Four Essential Freedoms of free software. Admittedly, it could even be true that a number of free licenses are not considered "open source" merely because they were never approved by the OSI.
Nonetheless, if software is released under a license which is approved by the FSF but not by the OSI, then that software is, in licensing terms, free but not open source. Perhaps one could consider a license as technically being open source through their own prudential study of its terms, but ultimately the OSI is the official judge of whether a license is or isn't open source, just as how the FSF officially judges whether a license is or isn't free/libre.