That sounds like the Diane we have come to know in the Return. 

Wait wait, was that voice actually in the Missing Pieces as released years ago? (If so, wowzers!) Or did someone just plop it in and put this video on Youtube recently? The timing seemed a tad forced at the end.

Under the video, I wrote "with extra audio 😉 " .

Someone added 2017 Diane voice on the Missing Piece video, found this today on Youtube.

It's a joke of course.

Ok. Good good. Thought I was goin nuts. I vaguely remember watching the scenes years ago and seeing Coop talking without response.

Funny. Loved her last statement (even if predictable ?). 

that's one major element that REALLY bothered me about the Return.

At the end of Season 2, Cooper goes into the Red Room going after Annie.

In Season 3 he becomes Cooper again after shoving a fork into an electrical socket.
Suddenly he has the hots for Diane?  I mean.. did he reconsider Annie after being in there for 25ish years?

It was like.. a "forced" relationship with Diane.  I never saw any evidence that he was ever in love with her at all.