It was named for its resemblance to another moth with a variation of verbascum in the specific epithet- perhaps Cucullia verbasci?

Okay, I'll take two guesses.
My first guess is that A. verbascoides doesn't feed on mullein, as most Apamea species with known hosts feed on grasses and sedges. If it did feed on mullein, I suspect it would feed on a number of other plants also, and, like the polyphagous Yellow-headed Cutworm and Glassy Cutworm, would probably be more common and/or widespread than it is.
My second guess is that the type specimen of A. verbascoides was resting on a mullein plant when it was collected. A shot in the dark, but there's more than one precedent from the bird world - example: the Magnolia Warbler breeds in northern coniferous forests but got its name from Alexander Wilson who collected a specimen from a magnolia tree in Mississippi in 1810 (during migration and in winter, the bird can be found in any type of tree).
Of course, I have no idea but it was fun guessing!