I wouldn't let one pro photographers opinion get to you too much,
You could aim to be an expert with all types of lighting, you could choose to specialise in flash or video lights or daylight or desk lamps...
The important thing (as you thought you knew) is to learn about light, how it works, how the direction and quality of it change the shape of an object / subject.
Sticking to 'natural light' because you don't understand flash or are scared to try or learn, is a completely different thing to having a preference for shooting in natural light because you appreciate the skill required to bet the most from it.
In the same way that choosing to shoot film because you can be sloppy with your exposures and the magic lab machine will give you OK prints is different to choosing film because you appreciate how it'll render your shadow detail and if you pull or push it in different directions it gives you immense image control.
Learn to shoot with windowlight and reflectors, when you get frustrated that you can't get what you want, explore flash as a tool to give you more control no matter what conditions you're faced with.
But most importantly, whilst you're learning and practising, enjoy yourself, that's what it's all about. And ignore anyone who says Canon/Nikon, Manual/Auto, Flash/Natural, Film/Digital is in any way an obvious choice.