Since the information that has been given can be sourced from two different and mostly reliable Pokémon information resources, we can assume that Population Bomb truly is a slicing move. From what I've seen, Population Bomb being a slicing move likely derives from its Japanese origin, ネズミざん , which is usually written as Proliferation, however, can also be interpreted as "mouse cut".
The Japanese name of the move, ネズミざん, can be read either to mean “proliferation” or “mouse cut”
I believe it's a pun in Japanese where it can also mean "mouse cut".
So, Population Bomb being regarded as a slicing move likely is a little easter egg using wordplay, because Maushold can never have the ability Sharpness in normal circumstances, and a Pokemon with the Sharpness ability may never naturally learn the move Population Bomb. Basically, Pop. Bomb is a slicing move because of a little pun.
Source (top and third to top comment)
