He's saying that, even though he changed the message, the signature still validated. He doesn't realize that the resulting GPG file contains the message, so it's verifying it against its own, stored copy.
That's what I thought, but couldn't confirm. Basically he's verifying a valid file and inferring it relates to a different file.
Sounds like a UX problem than a technical one. It's equivalent to me zipping up a folder, changing the contents of that folder, then expecting the zip file to have the change as well.
Funny you mention 'they'. I usually do that but noticed in one of my replies I used 'he'. Turns out I reciprocate what other's say without thinking about it.
