I've received one or two alerts like this one before, and today I just received two more.
One of the plugins reported was the WordPress Importer and the other one was for the Events Manager plugin.
I think that the difference might be coming due to the fact that you compare the trunk version of a plugin with the version installed locally.
Some(maybe even most) plugins actually have a development version in the trunk directory and then just supply the "Stable tag:" header in their readme file.
That's a minor issue and I feel like to fix it you might have to do some extra logic in your servers(since I assume the version check comes from your servers), but I just thought that it would be good to report it.