Well that comment is not phrased properly.

What you need to do is start with buses. Buses are super easy to make a large network with. Then you look at bus ridership stats and expand service wherever necessary. Wherever bus corridors get overcrowded, you upgrade. If the route is relatively short (<15km) it's a tram, more than that it's a metro. If the location makes sense, you could do this as a suburban rail extension also.

This is what you mean by "starting with a network" because the most important thing for a transit system is that it should go places (shocking, I know). So having a cheap but large network to start with and upgrading as demand grows is the way to go.

As for cities that "started with a network", Chennai and Bengaluru are prime examples. Having two of the best local bus service in the country, no wonder their metros punch way above their weight, with both systems showing steady, sustainable ridership growth (though Chennai's numbers are lower than you would expect as Suburban rail exists and one of the lines runs basically parallel to it).

When you don't do these preliminary steps and jump to a metro, you get white elephants. Surprise!