Well, it was a stupid move on Webbers part... if he was coming up on a slower car he should have expected that car not to see him right away and waited for a better place to pass... but I wouldn't say it's completely his fault. If you look really close at the video it looks like Kovalinin hit the brakes early and started moving over for Webber right about the same time Webber started moving to go outside and go around him. Webber clearly wasn't expecting him to brake that early and change direction and he had to try and go back to the other side and simply didn't have enough time to react.

Any good driver knows, it is the faster cars responsibility to safely pass the slower car. The slower car is supposed to hold their line and not make sudden changes. Same shit that happened in the 24hr Lemans when one of the prototypes tried to pass a GT2 car (ferrari if I remember right). The slower guy saw him at the last second and tried to get out of the way when the other guy was already committed. These are professional drivers out there. Kovalinin should have known better.