I agree to the possible definition as being only an empowered arcane focus, though I still think it is a firearm. Either way, WotC really needs to address this better. A sage advice article would do, even though those are sometimes totally wrong. The writers and editors chose the word firearm. Perhaps it was a poor choice of words, because firearm does have a meaning, that being a firearm. A different name for the feature and the item would be more concise in the case of it being not-a-firearm; perhaps Artificer Focus or Artillerist Focus. This should have come up in playtest. But it isn't the first-time poor writing/design and editing have occurred. Nor a lack of playtesting. Especially in the Eberon and Tasha's books.