Because they are not the same thing.
Mining means miming to a complete vocal track. Lip synching is singing along to some of the track, with the tricky notes coming in at strategic times. If you notice, some of the very top notes for which MC is famous kept coming in on the music backing track, what was missing was her guide vocal, and she obviously hadn't rehearsed learning the track, so she was left looking foolish fo what must have felt like an eternity.
I would like to have been any of her 'people' when she got off stage!!