When I do a cmd-F on this page I don't find the word "muppet" anywhere. This is clearly an oversight and one which I'm now remedying.
But seriously:
Before you delete a folder, open it to see what's in there.
The sheer volume of stuff in usr/ should have been a bit of a giveaway. They would have included some files with very hairy-looking names, quite a lot of files called applesomethingorother, and modification dates corresponding to the day your OS was installed - or earlier.
And They Said the Mac Was Intuitive