Both could be correct. Here I think "day" could make more sense. An example of the other case: "Back in the days of Fortran programming..."

If you leave out anything after "days" by just saying "back in the days" then it is like you are pausing. As in when you reminisce, "Oh, back in the days!" Maybe that is what the intention was.

In any case, the commentor was actually just saying that he thinks nothing has changed.