Consider it like era's/decades. It doesn't have to be perfectly accurate but it gives you a rough idea of a point in time. When I think 'web 2' I think of Digg, Facebook, social media. At the time it was more of a buzzword but in retrospect it defines that era. It doesn't have anything to do with 'versioning' the web.

100%.

The web evolved constantly from birth and became more interactive over time.

I always hated that silly “web 2.0” branding.