I was initially less than comfortable with this usage (“sole progenitor”) but it makes sense within the discussion of what it means to be “human” in the biblical, elective and salvific sense. In other words, if God started the ball rolling on the new creation through whatever endowment he gave Adam and Eve (over and above what they shared with “those outside the garden”) then in that important sense they are the sole progenitors of humanity (seen as Homo divinus, if you like, which is the status of all humanity now).
To give a sci-fi genetic comparison: in a laboratory accident Dr Yevrag acquires the mutation that makes him telepathic and telekinetic, and that gene gradually becomes fixed in the population through his offspring. He is the “sole progenitor” of Homo telepathicus, if that characteristic becomes the marker of a totally new kind of life for the human race.
That, at least, is how I give the term elbow room!