I have a strong accent and I moved to a part of the country that it was common to have a totally different but equally as strong accent. Even though me and my neighbours were all speaking the same language, we could barely understand what each other were saying, no one was offended, it was funny. It’s not racist, sometimes people are hard to understand with strong accents. If you’re worried about the fact you mistook him for a telesalesman, the amount of scam calls people get these days, it’s understandable. I expect the staff at the restaurant had a good laugh over it and weren’t offended. Don’t worry so much.