Earlier quoted context omitted.
Are Craigslist or Ebay software companies? They obviously need software to run, but like Google who are mainly in the ad business, these people are in the matchmaking/social business not software business --unless they were to sell their software to other parties who were user/client-facing.
I think of it like this: would the business exist without the software they wrote in house to facilitate the business? If the business ceases to exist without the software: it's a software company.
The local steel mill got hit with ransomware a few months ago. The Windows virus didn't touch the furnace controls, cranes, sand dispensers, or forklifts, but it shut down their custom software that lets them receive purchasing requests, queue work orders to the foreman, and eventually ship to and bill customers, and they were shut down for weeks.
Is a steel mill a software company?
I suppose the local Amish bakery/furniture store might continue to accept cash if their borrowed battery-powered POS terminal went offline, but every other business I can think of from Boeing to Wal-Mart relies on software to facilitate the business. And at various levels of scale, they all grow from purely running on an Office license to some custom spreadsheet logic to an in-house database server.