This is only true if Airbnb creates demand for owner-absent short term house lets. Otherwise it's just a platform taking market share from other platforms like VRBO or Craigslist and the amount of housing supply would be the same with or without Airbnb.

And of course it is the latter. The great majority of listings on the platform are for owner occupied dwellings where a room, loft, basement, or guest house is being let out. This does not keep supply of housing suppressed.