I don't think it necessarily means using it in production but rather using it on some non-trivial capacity that exposes you to it's various complexities and nua

I don't think it necessarily means using it in production but rather using it on some non-trivial capacity that exposes you to it's various complexities and nuances such that you have more than just a surface level understanding. That probably coincides with using things in production a lot of the time, but that's not strictly necessary.