Well for the Crabrawler family it's just because they're crabs. Land crabs, yes, (ones which actually drown if placed in water...) but I guess they're going for some kind of ancestral hereditary thing. *shrugs*
Emboar is a bit of a stretch, there's a loose connection of it being a pig, pigs like rolling around in mud, mud is a mixture of dirt & water, and since Emboar is Fire-type it can heat the water. Also, since it fires flames from its nose, I guess they also concluded it could do the same with water; either filtering it from mud it breathes in or its Scald if actually super heated snot.
Some more Scald oddities:
1. Two Pokemon learn it via level-up: Panpour family & Volcanion. Volcanion makes sense, but why the Panpour family?
2. And why can't these Water-types learn it via level-up: Chinchou family (heat the water with electricity), Remoraid family (they're based on firearms), & Clauncher family (based on the snapping/pistol shrimp, a shrimp who can snap its claw so fast it superheats water by creating a vacuum).
And another thing I noticed: Why doesn't Qwilfish, a Pokemon partially based on navel mines, not learn Self-destruct or Explosion by level-up?