She probably felt entitled to treat him like shit because of his job. I encountered it myself when I used to do part time driving work.
In the minds of a great deal of women, a man's value as a person, as a human is anchored to his job. The contempt is especially noticeable in younger women. You might assume that older/married/rich women would be bitchier but this is not the case. The more mature person is more likely to understand that an individual's personality, intelligence, morality, goodness, wit – their value as a human – is not dictated by their job, at least in most cases (some do use their career as the foundation of SELF). I had some really long conversations with older women (30+), often along the lines of "user, why are you doing this job?". That's one of the few perks of low paid casual work, if you're lucky then your level of responsibility and deadline pressure are commensurate, i.e relaxed, and being a delivery driver frees you from the mind-numbing environment of a production line. It's not every day you can go to work and have a 20 minute chat with a woman of 104 years of age, who is still fit enough to tend her garden and has wartime stories to share about her time as an air traffic controller in the RAF.
Anyway, back to the point. The experience with young women is polar opposite. Open insults, abusive behavior, mocking of your personal appearance, hair, clothing, voice, tipping £0.01, the Bong equivalent of 1 cent and before someone says it, no I'm not a hog/beast/pig. These same girls would have had mucous dribbling down the inside of their flushed thighs if they bumped into me suited and booted during normal daily life because I'm not a bad looking lad + 6`2. You do get the opposite effect sometimes, I should add for balance: the 16-year-old whose parents are out, inviting you in for example.
So back to the case. Relative social status is everything. She viewed herself as of higher status than the driver, therefore she can abuse him without repercussions. The exact same man, in the exact same car, with the exact same bobble head, would instead be the target of cutesy flirting, blushes and have a damp spot left on his seat, if the situation were such that his perceived social ranking was higher than hers (by social or financial means), example, respectively: university professor giving some students a lift home or random man flagged down for a lift, who happened to have $20k and a block of cocaine sitting on the dash.
Dealing with young women is very hit or miss but so many of them are cunts that it's better to keep them out of your professional life.