GPT creates plausible looking sentences, it has no concept of truth or anything like that. Since if you have an “an” it’s overwhelmingly likely that the next word will begin with a vowel it will choose one which plausibly fits with the corpus of text that came before. Likewise for an “a”.

There is no compromise in ability. It doesn’t have anything to “say” or whatever. What it produces is more like nonsense poetry than speech.