Proplyds should be young molecular ( ejected star spot) black holes accelerated by plasma tails.
Proto planetary discs, show mostly a tail and seem to be in motion in opposite direction of that tail.
Why because most proplyds show strong resemblance with some Helix "proplyds". and we know that the Helix nebula is the result of a star explosion see image:
as the next Bok globule image shows.
The origin of micro molecular black holes as exploded ( ejected) star spot black holes.
Star spots however are assumed to be the result of crashed Comets in the former star.