I think UAP is an attempt to be more general and not include implicit assumptions.

A UFO is unidentified, but it might not actually be "flying", and it might not actually be something that can be considered an "object".

I don't have the slightest idea about the acronym change.

0xbitcoiner

I still call them UFOs. I find it interesting that the acronym has been changed. Was this done to create confusion, make it sound more legit, or some other reason?