1) Exiting Turn 13 there was a legitimate overtaking opportunity for Lewis Hamilton as his speed was greater than Jensen Button’s.
2) Both drivers took lines substantially similar to many of the other drivers, and did not move as far to the left as the preceding driver, Michael Schumacher. At the moment afte Hamilton moved to the left to pass, Button looked into his mirror. It appears from the position of Hamilton at that moment [and is confirmed by the drivers] that Button was unlikely to have seen Hamilton.
3) At the point of contact Button had not yet moved as far to the left of the track as he had on the previous lap, or that Schumacher had on that lap.
The Stewards have concluded that it was reasonable for Hamilton to believe that Button would have seen him and that he could have made the passing manoeuvre. Further, the Stewards have concluded that it is reasonable to believe that Button was not aware of Hamilton’s position to his left. Therefore, the Stewards decide that this was a “racing incident” and have taken no further action.