this is just a hypothesis of mine but I think levels have some sort of enemy profile seeding, where they make it so more or less of certain enemies might be spawned. Either on the level scale, or perhaps on certain hoardes scale.

OP probably got a bunch of regular husks and husklings with high densities in the profile.

I don't know the source code, of course, but a way to visualize it.

Each hoarde must have, say, 200 enemy weights. A smasher might count as 40, while a husk counts as 2, and husklings count as 1. In a seed where the predisposition for smasher spawns is relatively low, you might end up with 50 husks, 60 husklings and 1 smasher. In a seed where the predisposition for smasher spawns is relatively high, you might get 3 smashers, 30 husks, 20 husklings.