its good that you are vigilant, but distance to "point where two or more planes are cleared to same level" also has to be counted in. Thus there are just two posibilities with your case,
a) ATCO error
b) intent to start descent of preceeding traffic before you come into scene
in both cases you should look out for our mistakes, as we are for yours. To eliminate them that is, not to put anybody on the shame list
