Really?
My understanding is, it was applied primarily to the allegedly heretical Christians. That would include Christian converts from other faiths, most notably the Jewish Conversos in Spain. It would not apply to non-Christians. In fact, an apostasy would often terminate the case, since the issue of heresy would be rendered moot.
What you write is true, and contradicts only what I said if you take what I said out of context. The real target of the Inquisition were those Moslems falsely claiming conversion. Not so much as heretics, but infiltrators.