using じゃない in の言葉じゃないけど for affirmation?

Question

Recently, I came across an interesting case of じゃない usage, which I haven't seen prior.

さっきの連中の言葉じゃないけど、卒業したくねーわー、オレ。

In the example above, the sentence itself makes sense only in case of じゃない having an affirmative connotation. Through some searching, I also came across an article, that had a direct quote from Shakespeare using the same construction as in the example above

シェイクスピアの言葉じゃないけど、善悪って存在するものではなく、人間が作り出しているだけ。nothing either good or bad, but thinking makes it so.ってね。

Although I get that in this case じゃない isn't here for the purpose of negation, I don't quite understand what exactly is the grammar behind it. The only plausible explanation I can come up with, is something like かと思う being omitted after じゃない, like in

さっきの連中の言葉じゃないかと思うけど、卒業したくねーわー、オレ。

Am I thinking in the right direction, or is this じゃない usage something completely different?

Edit: or is it used to show that the speaker wants to quote someone, while knowing that the quote he makes isn't word-for-word?

Answer 1

Grammatically speaking, this じゃない is a negation. This Xじゃないけど is a kind of set phrase that typically implies "I don't mean to directly quote from X, but I feel the same thing as what X said", "What I'm saying happens to be similar to what X said, but I want to say this as my own words", "You may be remined of what X said, but this is what I am thinking now", etc.

Sometimes, Xじゃないけど is used intentionally while evidently quoting someone's famous statement or mimicking someone's signature gag. In such cases, it may be like saying "no pun intended" when a pun is intended, so you shouldn't take it literally. Your second sentence about Shakespeare may be an example of this (I don't know whether Shakespeare really said this, though).