Similarly to how a Postdoc researcher is a researcher, I think that a PhD student should be considered a researcher. Especially when:
- A salary is obtained for the research that is done as part of the PhD studies. Per definition, I would say that students pay, they are not paid.
- A research master has been studied before and there are no lessons, classes, exams, etc. So in fact the person is not a student, but "at least" an "apprentice".
I know that naming things in one way or another may not make a big difference for those in academia that read the CV, but it may evoke different ideas for those out of academia that read it.
As far as I know, they are absolutely equivalent, even if one is more used than the other (mistakenly, IMHO). Nevertheless, I would like to get confirmation, if possible from an authoritative source (like a dictionary for titles), and at the same time I think that the question may be useful for many people.