I've been working in game development for almsot 15 years in one way or another mostly as Artist/Designer, even worked on big titles like Battlefield: Bad Company during my time at Dice, but for being an indie game developer I'm still a beginner. Currently working on my frist game which I made from scratch in construct 2.
I guess it's partly a matter of skill, experience and success. I wouldn't expect to call myself a proper indie game developer until I had some success to be able to live from the profits. Even then..... A hobbyist could also have a success with a game made in the spare time, but that doesn't automaticly make him/her a proper indie developer unless he intend to continue on the path of creating games.
Another way of earning the title would probably be if you're already a known name in the industry and have been working with other studios in a leading role, then setting up your own studio, or get a job at a known studio.
Last but not least. There are some highly skilled people with some experience that can call them self indie developers even before releasing any game (But usually well in to production). Those people know how to market themselves, and can present a polished product, and already has tons of followers even before releasing the game. Those people created a hype around their product even before it was done.
Anyway ... Keep going at it. I think your best bet to becoming a "recognised" indie developer is either by showing up sales numbers, so keep working on it.