I can't see that there's anything either unlawful or even unethical in the practice.
When I worked on the railways my contract said that I was a 'Senior Team Member'. My bosses and colleagues referred to me as a 'Station Supervisor'. My badge simply said 'Customer Services' (which, incidentally was exactly the same as what appeared on the badges of my junior platform colleagues and even on those of the cleaning staff). Staff doing exactly the same job as me at a station just along the line from us were referred to as 'Station Managers' but at a small intermediate station the 'Senior Team Members' had hardly any supervisory responsibilities to carry out.
Things got even more complicated when we merged our operations with those of another company. There were some 'Managers' who couldn't even sign an authorisation to pay £10 for a taxi, whereas there were 'Supervisors' (such as myself) who could sign away thousands of pounds on rail replacement buses on a regular basis!
Your 'General Assistant' label is probably a 'grade' within the company (which could be applied to people doing a variety of jobs), whereas your 'Driver' title is a description of the work that you do within that grade.