A "computer company" is one which makes something computer related for sale (hardware or software) as it's primary business.
Software is Uber's primary business. Opentable isn't a restaurant, they are a software as a service operating in the restaurant industry. Golfnow isn't a golf company, they are software company in the golf industry. Uber is the same thing. They may be targeting a certain industry, but ultimately they are a software company servicing that industry.