This is a good example of a good bike handler making a mistake, tackling the corner too fast, but using his skills to save himself.
There are the skills of descending with the bike handling but also the mental judgement of how much to push, how fast to go around corners. A rider can have good skills but if they over estimate how fast they can tackle corners they might crash a lot more than a rider who has worse skills but rides to those skills.
Sprinters are probably amongst the best bike handlers but we do not get to see them descend as often. One I do remember is Thor Hushovd descending by himself in the rain on a tour de france stage which was pretty impressive. Not sure which year even.
Riding on cobbles is a skill in itself.
I agree with the Sagan and Nibali, the whole Liquigas team (minus Basso) seemed to be quite good. Perhaps having Nibali on the team helped them all, especially if he pushed the on training rides.