I mean exactly the sound that is referred to as the "rolling R" or "[r]" in the original article. The flap is [ɾ]. In any case, as the sister comment says, th

I mean exactly the sound that is referred to as the "rolling R" or "[r]" in the original article. The flap is [ɾ]. In any case, as the sister comment says, the point is that in order to learn the rolling r (consciously, as an older person) you have to notice the flap, and repeated flapping can transfer into the rolled r. So, yes, you learn the flap first, but few people start out saying "I wish I could flap my rs," instead they're looking to learn how to roll them.