A sommelier should have some qualifications in the study of wine to be called a sommelier. The problem is there are many organisations that can give some one the bit of paper to call themselves a sommelier.
So someone acting as a sommelier but without an acceptable piece of paper could be called a wine consultant as they usually have some experience in the service of wine.
It is interesting to look through the job advertisements for sommeliers on cruise ships to see what the requirements are, Here is one place to look.
https://www.allcruisejobs.com/search/sommelier/
The line with the most stringent qualification requirements at present is Costa. They require a sommelier degree.
Seabourn require an assistant sommellier to have a class 3 WSET award in wines whereas Silversea just says a WSET qualifications. Personally I would regard a sommelier as having a WSET class 4 Diploma as minimum requirement.
https://www.wsetglobal.com/qualifications/?subject=Wine
Ritz Carlton yachts only require a WSET class 2 certificate to be a Sommelier.
Of current ads RCL.Viking.Azamara and windstar don't require any wine education to be a sommelier.
Like many things with wine there is some pretentiousness in these terms. Ironic as most sources say that the name sommelier is derived from the old French word for mule driver.