I think you're looking into what an 'induction kit' is too much.
An air filter is just a filter, nuff said.
An induction kit is a filter, plus whatever else is needed to make it fit / plumb pipework together etc.
In this case, the 'induction kit' that company make for your car, consists of joining the filter to the standard airbox.
however, there's loads of different types and brands of induction kit.
My golf for example, a K&N 'induction kit' consists of an air filter, a rubber hose and 2 clips to bolt the filter straight on.
The kit i have consists of a massive alloy pipe which leads the filter down into the bumper.
They're both still induction kits, you just need to do your research first to make sure you know what you're buying