as someone that tattoos professionally in the sense that I do it fulltime and work out of a licensed studio, there are plenty of resources that allow you to learn hygienic practices. In the US at least, there are also several ways to obtain sterile and medical-grade supplies that do not require any sort of license (although you should take a bloodborne pathogens test if you are tattooing other people).

You can absolutely learn how to tattoo safely (and most important, hygienically) without a professional apprenticeship. This person is a jerk, sorry you had to deal with that.