Gromit is using hyperbolic language to eke out a wrong stance.
The two people were the authors of the situation they found themselves in - had they acted reasonably, as the vast majority of people would, the situation would not have escalated as it did.
The man was laughing as he pulled up - he was laughing at a policeman undertaking his job, and other than comedians, that would irritate anybody undertaking their job.
The woman then went into screaming banshee-mode which escalated it further; the WPC was heard saying to her something along the lines of ‘it doesn’t have to be this way’.
Gromit states they had been pulled over 15 times as though it is fact; presumably the two people concerned mentioned that number - why should we believe them?
I’ve no sympathy; had they acted reasonably, so would the police.