In Import > Pick File > PLY Import Options, there is a drop-down menu for picking the units of the PLY file, selecting “Millimeters” vs. “Feet” doesn’t behave as expected, same behavior regardless of input. Appears to default to Millimeters in all cases.
Latest Version 6 WIP (6.15.19099.12046, 2019-04-09), 2013 MBP 13"