That is what I inferred, but it seems a bit ungentlemanly to jump to that conclusion after merely picking “GNU” and “gnuplot” up in a sentence and nothing more, which is what most likely happened.
1. Conclude that its 90% likely to be what happened.
2. Not burden someone by asking a question you don’t need the answer to.
3. Disclaim credit for work you don’t lead.
Maybe you are far too pre-assumtpive that there was any ill effect, or even ill intent, in the statement being made, especially if the same fact is accounted for in gnuplot FAQ.
I guess "GNU, but gnuplot is not GNU" could be one, but perhaps at that hectic moment RMS didn't consider that option!
No longer than, say, adding GNU/to the front of GNU/Linux.