Dang, thats kinda cool and freaky all at the same time ya know. I never got that when i installed AT 6, beta or public release.....have to wonder who else might be seeing that.....that could scare someone who's not too familiar with computers.
I'm guessing that this could have been an error about trying to update from the Software Update CP. I'm even going to say that one of the code developers from Apple was going to pass testing of the final version on to someone else, developing QT6, who would input an appropriate error message in replace of the little statement he was given, and he just forgot about it. It's a guess, but IMBA (In my best assumption) that may be why the message displays that.
Try downloading the entire update directly off Apple.