You are not a beginner to ask a question like this, so if someone put something in the quote it will certainly not be considered plagiarism, as far as I know it never was. I also agree that it would be better to cite the source, but even without that, the intention is seen that the user did not want to present that part of the text as something that is his work.

Here is an example that I reported as plagiarism, and which stood unhandled for as long as 8 days, until I posted it publicly, and the user subsequently edited the post. If it wasn't plagiarism (and obviously global mods/admins think so), then what you have doubts about has nothing to do with plagiarism (by forum standards).