That's a really insightful comment that has turned my thinking on this area of economics on its head. It sounds like any business is capital intensive if it involves paying lots of people high salaries in order to do it, even if the salaries are the business's main cost.
Of course, software development doesn't have to start out capital intensive. A couple of kids working on their startup in a cheap apartment can work cheaply. They can defer the capital intensive part until they are successful. An airline doesn't have that option.
Capital is not necessarily money paid. If those two kids have the talent to create a successful website they are incurring opportunity costs due to the fact that they could be earning a decent salary with those skills rather than creating a startup.
Of course, software development doesn't have to start out capital intensive. A couple of kids working on their startup in a cheap apartment can work cheaply. They can defer the capital intensive part until they are successful. An airline doesn't have that option.