That's a bad example though. If airbnb.com is taken, should you take airbnb.io or airmatressandbreakfast.com? Paul's argument is: neither, get a different short name for which you can get the .com.
I take it that the article is aimed at early stage startups and is premised on the idea that choosing a name is worth about 20 minutes of time by a founding team and an experienced investor. I find Airbnb useful because "air" has nothing to do with the current company. Any connotations to air mattresses are probably non-positive at this point and the company's success came after pivoting away from low quality low cost accommodations.