Bottas did speculate not react!
According to studies Bottas´ reaction time would be twice as slow, as what would be possible for a human being.
Other than the current record in an official sports tournament for a reaction to an acustical signal - 0.101 seconds in the 1999 world championship of athletics by Bruny Surin in a 100m semi-final - there seems to be enough evidence to argue for Valtteri Bottas jumping the start in the 2017 austrian GP.
As you can see in the following video, Bottas did start in the exact frame, when the lights went out.
Current cameras record at a minimum of a 24 frames per second shutter speed since this is the lowest number of pictures per second that generates a sense of motion in our mind. Dividing a second by this number of frames gives us 0.0416 seconds. And that´s just not enough to actually react to an optical signal.
So, he jumped the start... but the F1 regulations don´t punish an expected start. Other sports like athletics do.