Indicates to me that they’ve never seen a word or phrase in print. It’s the opposite of a guy I knew that was seriously dyslexic, and would say things he’d seen in print, but never heard pronounced.
She was a very smart lady and a teacher. She had learned English in High School and University, but all of her teachers had learned the same way. To wit from nonnative speakers of English. My wife could read and comprehend the written English, but the way she pronounced the words was often humorous.