It does not make sense to me that "bivy" can be used for what is essentially a sleeping bag cover. And it would be a miserable mistake to make, taking a water resistant six ounce sleeping bag cover and using it as a standalone bivy.

And no, nothing personal was intended... I've met people who can't seem to parse the instructions that came with a tent, let alone what's said on forums, and it does pay to be clear about the differences between similar items that are intended to be used differently.