I disbelieve by default anything anybody says about their own language.
Sometimes a native speaker will tell you what a word means, and that it means only that but you can plainly hear the same word used in other ways, too. Sometimes he or she will tell you that two sounds are the same, or different when you can hear that they're not.
Most people seem to believe that their language is more difficult than yours. There's no sense trying to disabuse anybody. It's probably just an expression of cultural pride.
In the earliest stages of my Romanian, I asked a friend about the word "o," because I'd it seen in print but had not found it in my dictionary. He said it's not a word. He didn't try to explain why it's a common part of a sentence; he just said that it's not a word. It's one of two definite articles a cognate of "a/an." It's one of the most important words. Its usage is complicated but it's not "not a word."
Never trust a native speaker and stay away from the bilingual.