Q:

Was I wrong to roll back this edit?

I rolled back this edit.  There were two reasons.
Firstly, the included text is not relevant, because it refers to modules compiled into a program ("if you were to incorporate them both in a larger program"), not programs calling other programs, so it's not relevant to the question as asked ("by putting it in a separate, standalone program?").
But secondly and more importantly, this is a substantial edit.  It introduces text that the original author didn't see fit to use, and makes an argument that the original author didn't see fit to make.  If an edit like this was made to one of my answers I would immediately roll it back.  If the edit's author wants to make this particular argument, as I see it, (s)he should write a new answer and make it.  I cannot see that anything is gained by putting these words in the answer's author's mouth, when the speaker is free to put them in his/her own.
Two other reasons make me post here.  Firstly, I'm not the One True Arbiter of what edits are and aren't appropriate, and I note that the edit was approved by two respected community members.  Secondly, I'm the author of the main competing answer, so there may well be a perception of conflict of interest as a result.
So I'm being very clear about what I've done and why, in case the community wishes to take a view on it; I'm looking particularly for clear guidance on my second reason for the revert.  I would prefer it if we could get some kind of resolution here before starting a Wikipedia-esque revert war, but of course anyone with edit powers can unilaterally act (hence the problem!).

A:

Ooooooooooooh. A meta post. :P
Rollbacks are a privilege that is awarded with editing. In practice, they are almost no different from any other edit, aside from being a convenient one-click solution. When you are awarded that privilege, you are free to use it in any way you wish - you earned it!
That said, let me chime in on the edit. The edit already addressed the GPL FAQs, so it's unlikely that the author missed any information in the edit. Reading the answer closely, I agree with you that the edit doesn't feel relevant content wise. That edit was also substantial enough to be an answer of it's own. And a brief look at the post shows that the editor was involved before hand with the post, and that the edit wasn't called for or recommended by the original author. It was out of the blue.
TLDR
 The edit wasn't right. Didn't fit in content-wise, or context-wise, and it wasn't called for. It should've been an answer of its own.

A:

Chiming in here, as one of the reviewers that approved that edit. My original thought was that it helped flesh out the answer, and just inlined text the OP had linked to. 
After re-reading the post and going through your rationalization, I stand corrected. This was not a good edit, and should have indeed be rolled back.

