I haven't read the article but the terms 'fair', 'good', 'great' are so subjective that they are pretty meaningless. The first question I would ask is whether or not you want to be considered fit as compared to the average population. The fact that you CAN run 10K would sugggest in those terms, you are well above average.
However, you may want to compare your fitness to other people who consciously try to keep fit. So how do you compare your fitness as a runner with that of a swimmer, or a tennis player? OK, not an easy comparison. Maybe you can do it by a whole bunch of medical measures like Body Fat composition, resting heart rate, lung peak flow tests. But that's just numbers and doesn't equate to anything tangible.
So perhaps the only meaningful comparison you can make is against other runners. Then you have the trouble of saying, is someone who runs 400m hurdles fitter than a marathoner? So, really, the only way I know that allows for a meaningful comparison is to take race times and put them against Age Grading Tables.
Here's an example. Put in your age and gender, and you can put in race times or a percentage level, to show what % of runners can run at that speed. This is a great way of getting a better feel for how 'fit' you are.