Libre more specifically means the GNU licenses, as GNU didn't like that licenses like MIT were being called FOSS, as they don't preserve user freedoms like (A|L)GPL do.
Stallman wants people to say FLOSS to denote free software versus open source software, and my interpretation of this article is that he only deems the GNU licenses to be truly free (libre) software.
Stallman acknowledges the he did not invent the term, and describes how the "L" was added to connote freedom in the free-as-in-speech sense, rather than type of freedom the "F" was typically associated with.
FOSS was already a term to denote the other types of open source license like MIT, that is why FLOSS was specifically coined, to not only say that there is a difference in the word free, but also to differentiate GNU OSS license from the others.
