So actual release is Mint 19 (see lsb_release screenshot) Reported is Debian, wait for it........ "10" Yes that's right debian 10 has not been released yet (See 2nd screenshot circled part). I get the Debian part since mint isa hybrid based on debian and Ubuntu but I don't get the version or release number. FYI this is my local desktop machine too.
So yes I call this a bug. Umm I am afraid to update this system because I have no Idea how this could affect it. I also have had auto updates turned on in vmin but will turn that off. For I will only update through the real command line: sudo apt-get update && sudo apt-get upgrade.
TTYL & Have a good one. Doug