> While that's true, they seem to be saying that being a startup is not an immutable trait of a company, but rather a phase, and that any side project or solo business could enter the startup phase at any time.

I mostly agree with you, but I don't really agree with this idea. I mean, theoretically, yes, it's true - but I still think it makes sense to differentiate between a new restaurant, and someone trying to create a new technology product/company with billion dollar potential.

And this is what investors are looking for, too, which is why only this kind of startup gets VC money.