That's actually what I hear too, Elle. "Broken too," not "broke in two." (I never corrected Mandy's first post about it though.)
Just the way his inflection is, it sounds like he's referring to something else happening that would have been lucky--first the horse (ME!) being lucky to throw Jack, and then Ennis being lucky that the harmonica got broken, not just flattened.
Hmmm, we may have to call in Heath to answer this question! Enquiring minds want to know!