How so? Reincarnation is every bit as supernatural as Christian Heaven, and there are accompanying practices that are supposed to influence the outcome of that via karma.
I did not think impersonal entities were what the gp post was talking about; apologies if they were. But even including impersonal supernatural entities, the wikipedia page I cited shows that's not a defining characteristic.
It does not follow, from the claim that belief in supernatural entities is not a defining characteristic of religion, that the rejection of supernatural entities is a religion. You might be able to argue that they are orthogonal issues, but then a lot of religious people would disagree vehemently with you!