brings up many threads which indicate that, for previous versions, this was a WP bug
It is not now, and has never been, a "bug" in WordPress. The error has been misleading and confusing in the past, and the message can be caused by many possible circumstances, but it's not a "bug".
PCLZIP_ERR_BAD_FORMAT is a generic error that means, basically, the ZIP file that was downloaded is somehow broken. Many things can cause this. If WordPress.org was just down at the time, for example, then the download will timeout and the resulting file will be zero bytes long. Obviously, this is not a valid file and you get that error. Anything that causes the download to fail and an invalid file to be downloaded will cause it, basically.
So the question isn't whether it's a bug in the WordPress software or not, because it is definitely not. The question is why is your download of the ZIP file failing. I have no idea, frankly. Perhaps the host is unable to talk to WordPress.org properly. Maybe a guy in Idaho dug up the wrong fiber optic line. Who knows?
There have been times when WordPress.org was down, or times when it was heavily overloaded, and yes, at those times you might see this error. Currently, the site doesn't appear to be undergoing any extreme load, so I'd rule that out for now.
The error is a generic one, essentially, and doesn't lend towards explaining what the problem is, other than the website can't download the ZIP file properly.