When I worked for Nabisco, we had large robust sieves that would prepare flour being drawn from our 7-story flour towers prior to discharging into the weigh scales and mixers - several hundred pounds each batch. The contraptions looked like very large metal boxes that shook and rotated violently to sieve the flour. So it makes sense to me that a similar process would be recommended to pre-treat metal powders before being sintered into a 3D print.
In fact, a couple of challenges using powders in manufacturing processes are material purity and particle size. Apparently Farleygreene has introduced its SIEVGEN 400-US specifically to address these concerns for DMLS additive manufacturing.
When you are hitting a potentially explosive metal powder with a laser, powder consistency and purity are obviously important material attributes to control.