Sure, OSI has an official doctrine, and Perens has (or had) kind of a unique point of view within that, about the two terms being fully synonymous -- but he partly walked back that view later, and Stallman and FSF's has historically been very different:

https://www.gnu.org/philosophy/open-source-misses-the-point....

And especially:

"The two terms describe almost the same category of software, but they stand for views based on fundamentally different values. Open source is a development methodology; free software is a social movement.... Most discussion of 'open source' pays no attention to right and wrong, only to popularity and success..."

And of course OSI officially wrote "We realized it was time to dump the confrontational attitude that has been associated with 'free software' in the past and sell the idea strictly on the same pragmatic, business-case grounds that motivated Netscape." (http://web.archive.org/web/19981206185148/http://www.opensou...)

In other words, "open source" was about depoliticizing "free software" to make it more commercially palatable. (And arguably, it worked.)