Answer: Here's the rule.
There are three kinds of “person” in narrative for a story as far as writing is concerned:
First Person, I narrator. We are INSIDE the “I” character and see and hear (and taste and feel) whatever the “I” character does. Nothing can happen in the story unless the I narrator is there to see, act, or react.
Second Person, writing a letter, or addressing the reader directly as “you”. Second person is usually regarded as a mistake, though I've seen it done and done well.
Third Person, the viewpoint character is a “he” or “she”, or the given name, never “I” unless they are speaking, but the reader is still inside that character’s body, thinks with that character’s mind, and feels with that character’s heart.
Once you have established narrative person, you should not switch from one to the other in narrative, within the same story, with the exception that dialogue is usually written in first person as that is how someone would speak. And of course the rule applies to narrative, not to dialogue. "I think..." "I want..."
Direct thoughts of the viewpoint character, which appear in Italics in the ms., are also usually in first person, just as if the character has spoken aloud, but without the quotes. If the writer was reading their story aloud, it is possible that some of the first person stuff was thoughts and you just couldn't see the Italics as you had no page to follow them on.
Or maybe you're right and they just all mixed up. Who knows?