There's no objective method to determine how much "grind" there is in a game (albeit I really wish there were). However, if a game is too "grindy", then threads such as "mile wide, inch deep" start to pop up (or just plain "too much grind" threads, such as this).
I do believe ED suffers quite a bit from "too much grind" syndrome - making progress towards any of the latter ships takes a lot of time and repetition. Said repetition is the key problem here - in exploration, once you've seen one star system with 3 suns close to each other for visual awesomeness, you've seen them all. Once you've found a lucrative trade route, you've seen all trading has to offer (you can repeat the process of finding and exploiting a new trade route, but it'll be largely the same). Combat is a lot of fun and probably the most dynamic aspect - lots of things can go well or wrong, but even there patterns emerge after a while (especially true if you consider how many ships one needs to destroy on the way to Elite status). Finally, the game makes players wait a lot - wait for SC to charge, wait for jump to charge, wait to approach a station / destination in SC, wait for the bulletin board to load, wait for the dock animation to finish for outfitting... this definitely compounds the issue.
All of the above aren't bad in and of themselves, but combine it all and I can see why ED can be seen as "too grindy". Heck, I sometimes get fed up with it too.