He means that the virgin Mary; a.k.a. his "Jewish minx"; was more likely to be a liar than the Blessed Virgin Mary. She also is alleged to have said, that, henceforth all generations shall call me blessed. She didn't lie about that, for generations of human beings have been calling her by that name ever since.
Admittedly Hume suggested she was a lying "Jewish Minx", thereby proving both his stupid antisemitism and his antireligious biases in one dull-witted question.
Which is more likely (1) that all life "evolved" out of a big bang far more powerful than any modern atomic weapon or (2) a vacuum at 3 degrees Kelvin, or (3) as a consequence of a Deity suspending the "natural order" to the effect that FIRE sterilizes absolutely and that ABSOLUTE COLD is entirely antithetical to life?
Hume's well known prejudices and 1 honest Jewish Lady, as well as the well known "natural" order.