As a collie owner I have to correct some of your viewpoints:
The whole lunging at/attacking a car thing.
That’s a collie trait and no way suggests a vicious animal at all.
They are motivated by movement and often try to control/herd any fast moving things, like cars, bikes, even people etc.
It’s what they have been bred to do for generations.
A responsible owner would have trained the dog not to herd inappropriate items or had it leashed if unable to.
The ‘attack from behind’ is relevant.
Herding breeds often chase and nip/grip from behind.
The ‘slowed down’ argument is bizarre!
The bite could have happened for multiple reasons; fearful, redirected through frustration etc but if it was because of inappropriate herding, which is very common in collies, that is, the dog isn’t intending to harm you but is trying to ‘herd’ you/control your movement, slowing down would be the correct thing to do because when the item to be herded stops moving they often stop trying to herd it.
Collies are up there for biting, and I am a collie owner myself.
It’s often due to inappropriate herding behaviour or nervousness which is a known issue in the breed as they tend to be high strung.
If it is usually muzzled I wonder if it’s perhaps done similar before.