A startup usually comes with the connotation that you will scale it to some sort of ideal (whether that be revenue, the people or businesses you have an impact on, etc.). A site that pulls in a decent income via advertising is really just a lifestyle business with little chance of scaling. Now if you made a network of these sites or found some other scalable product coming from this site.. then you'd have a startup, no? No one says you have to build a startup though.
Merriam-Webster definition of Startup: "a fledgling business enterprise".
See a lot of zero revenue businesses that throw around the scale idea as justification for not having a business model, but the older I get the more I believe titles, whether for what your business is or what your role is, matter less than results.
What makes the startup world so exciting is its variety outside of the echo chambers: Food truck startups, jewelry startups, services startups. Many of which don't plan on or will never "scale" in a web sense, and then others that will scale in ways the founders couldn't imagine the first year or two out of the gate.