"Car" is merely used as the name of the sub group rather than a descriptor for the alt mode. Similar to how there are non-car Mini-Cars, such as Powerglide, Warpath, Seaspray and Cosmos! And while Swoop isn't a dinosaur, he is classified as a Dinobot. So while Grapple is not an Autobot car, he is an Autobot Car.

Although this makes me further appreciate why Combiner Wars Powerglide is now an Aerialbot, because A10 Thunderbolts aren't cars! Some people whinged about it, but it makes sense. Also why CW Blast Off is a fighter jet instead of a space shuttle... cos good luck winning a dogfight in a shuttle.