What sort of moron slams on the brakes & goes slow when on a long A6 straight they see the flashing blues of an emergency services vehicle coming the OPPOSITE way?
Yes, this kind of moron in a Seat Ibiza.
The car wouldn't impact your journey whatsoever. They weren't overtaking anything. You literally didn't even need to slow down never mind slamming the brakes on.
If you can't read the road you shouldn't be on the road. Tosspot.