This made me ponder a little. On one level, I agree that framing ones feelings around a day off from employment keeps us in work mode, but I cannot see how to look at it any other way. If I ever grow to view my days in retirement as nothing special, then I think I will be losing something that makes me feel good. So, I have no problem looking at my life as "vacation"; that is a good thing.Everyone's RE transition is different I think. Not everyone was happy to retire, some sort of ran out of options, etc.
I still maintain that you're not mentally retired until you STOP saying things like "everyday feels like vacation/Saturday"; you're still using work as your context and reference.
Once you leave that work context behind, you've really moved on to a new life.
Of course, YMMV