So now that you've told me what it does NOT mean, perhaps you can clarify what it DOES mean? I still don't understand.

In particular, the phrase "in the mind" implies that temperature requires a mind and would not exist if there were no minds around. Given that we are talking about classical systems, this seems an unusual position to take.

Another implication of "in the mind" is that different minds would see temperature differently. In fact, if you look into the original EY post, it explicitly says

Is the water colder, because we know more about it? Ignoring quantumness for the moment, the answer is: Yes! Yes it is!

And that makes me curious about phase changes. Can I freeze water into ice by knowing more about it? Note: not by doing things like separating molecules by energy and ending up with ice and electricity, but purely by knowing?