I'm pretty sure that the term Stromling is derived from Maelstromling and as such it makes sense to use it to refer to any Maelstrom Being. At the same time, the game generally only tends to name enemies as Stromlings when they're infected minifigures (or close enough). Maelstrom Dragons aren't Stromling Dragons and Dark Ronin aren't Stromlings either, which I personally ascribe to my headcanon that they're infected spirits rather than physical minifigures. Plus, there's the fact that the creatures called simply 'Stromlings' are the infected minifigures in the game (and the stories), so an implication that the two are connected could be there. And what with Darklings and Spiderlings also sharing in the -ling suffix, it kinda makes you want to refer to them all as distinct categories.
I think I'd suggest a double definition myself. Stromling can be used to describe any Maelstrom Being, but it's also often used to refer to infected minifigures exclusively as its own category of Maelstromlings.