מה לי מגוי מה לי מישראל להבדיל, שהרי שניהן תורת גזל נוהג בהן
Lest anyone think that Jews are the same as non-Jews, "lehavdil" comes to say that though someone may be drawing a comparison between them, they are truly incomparable.
The passage is found in Sefer Ra'avya, written by R Yoel's son. There there is no "lehavdil", and R Prof Victor Aptowitzer points out (no. 690, II p. 395, n. 4) that the word was surely added by a later scribe, since the expression is not a medieval one.
Anyway, in a manuscript of Teshuvot Maharam that I'm reading through now (ed. Berlin, p. 121, no. 54), the word is missing too.
Just thought I'd share that with you.