That is an incredibly bad retelling of the GNU story
This was not mentioned at all in the blog post.
You can infer it mattered, but you can also infer he was pissed he couldn't make the machine do what he wanted. These are both valid interpretations if the same story... Which is the "crux" is up to the teller.
There isn't really any other interpretation than that.
Also the story you linked at is not RMS' story, but a different and more recent story which is also about a printer that sounds similar to RMS'. The RMS story is linked in the page you gave, though it is a transcript and kinda big. Here is the relevant bits:
> And then I heard that somebody at Carnegie Mellon University had a copy of that software. So I was visiting there later, so I went to his office and I said, "Hi, I'm from MIT. Could I have a copy of the printer source code?" And he said "No, I promised not to give you a copy." [Laughter] I was stunned. I was so -- I was angry, and I had no idea how I could do justice to it. All I could think of was to turn around on my heel and walk out of his room. Maybe I slammed the door. [Laughter] And I thought about it later on, because I realized that I was seeing not just an isolated jerk, but a social phenomenon that was important and affected a lot of people.
Emphasis on the last bit: "And I thought about it later on, because I realized that I was seeing not just an isolated jerk, but a social phenomenon that was important and affected a lot of people."
And after all he made the Free Software Foundation, not Working Printers Foundation.
Stallman wanted an ecosystem he could control. Did it work? Sort of.