It's a GPG signature for the zip file. It's digital proof that the person who controls
this GPG key claims ownership of that file. And it's dated and encrypted to the file, which means if the file is changed the signature won't match.
I know how it works but since I was not able to access the link, I did not know the reason for the key. All looks good now 😉
Flag supported and left a negative feedback for the user too.
Good job in connecting him.