I think all of you need to check the "Feroz'ul Lughat", Patha means right hand / brilliant student etc when it comes to not attached to body.
Dictionary even says, Ullu ka patha = Ulla ka sha'gird (student of Ullu).
What my conclusion is, we as easterns think that Ullu is a bewaqoof bird and cannot teach reasons to its students, so its students will even be more foolish than Ullu itself is, so we call "Ulla ka patha" means even more foolish than an Ullu.