These are always difficult calls to make.
I haven't seen the video, but the way you've described it it sounds like it was still Hara's corner.
Two things to take into account in situations like this... Would the car that was trying to make the pass have been able to make the corner (i.e. reach the apex) at the speed they went into the corner, and had they actually got far enough alongside the car in front to claim position.
Basically, a clean pass will be where the passing car is side-by-side with the car ahead, and both make the apex without contact.
If the passing car can only get level by carrying way too much speed at the turn in point, and makes contact with the leader as he overshoots the corner, then it is a bad move. Normally, the leader can counter this by lifting off a little and letting the car trying to get past shoot by without making contact, then turn in on the racing line and keep first place.
If the passing car is too far behind, and ends up T-boning the leading car as the leader turns in, then it's also a bad move.
Normally it's the times when the cars are both carrying the right amount of speed into the corner, but the passing car is a few inches short of being level, that are hardest to judge. Generally if both cars can make the corner with no contact or very light contact, then it was a fair move in my book. So much of it just comes from experience of watching racing.