I believe Hamilton's poor start was due to the dampness on his side of the starting grid, I remember hearing that Mercedes had the starting box dried by the race marshalls because Lewis complained that it was too wet. I think Ferrari and Red Bull complained about this. So Lewis was sat in his starting position with the "damp" track in the back of his mind and overcompensated by letting his revs drop too low in an effort to prevent too much wheel spin at the moment of launch.
Just my take on things, but everyone on that side of the starting grid had poorer starts compared to the drier side of the grid.