One can have a monopoly without directly trying for it. Especially when it comes to services with a lot infrastructure involved. Once you make those investments, it's hard for anyone to compete against them.
A monopoly just means you control a significant amount of the market. I think, technically, they would fall under oligopoly. Where a few businesses have control of the market instead of just a single business. But the point is they have a far larger share of the market than most others. This is mostly because they create a product that people want to use, instead of making a service that unfairly captures the market through things like game exclusivity or hostile takeovers.