This behavior has been there since point snapping was introduced. It seems redundant but I'm sure it is this way by design. One is for the point object, the other is for the type of point snapping that's being done. If you toggle off the 'Existing Point' option in the selection bar, then quick pick will only show one object; the point object. In the datum plane by 3 points case, because the system is filtering selection to points or routing objects, you may turn off all point snapping and still be able to construct the plane by selecting the point objects.