I doubt that drivers at the right lane slow down coz of the ambulance.

Check again the video, Go forward (Green Light), Turn Right (Red)

Some driver on the right lane stopped coz Red light thus, make the unlucky driver thinks that they slowed down and stopped due to the red light.

Hope u guys understand, the unlucky driver doesn't really speeding in the left lane, but cars at the right lane stopped due to the traffic light.

In this case, the one fault for the driver is unable to mention the siren of the ambulance.
But I think this is common mistake as the ambulance suddenly popout from a blindspot.