Would a Mossberg Shockwave attached via a picatinny to picatinny adapter to an AR pistols handguard still be considered an AOW?

So you get a pistol, which didn't have a stock, and attach a Mossberg Shockwave, which is only considered a firearm, is it still an AOW? Not an SBS without a stock attached. Not a rifle since it's not a vertical grip and shouldn't affect OAL anyway. Is it an AOW or something else?