Similar discussions come up in workshop classrooms all the time. One person says something in a story isn't believable and another says, "Oh no, the same thing happened to me (or my brother, best friend, dog) and it happened exactly like this."
I think the discussions actually miss the point.
The question isn't 'can you believe it?' but 'is it believable for this character?'
To paraphrase Shakespeare (because I'm not going to get the quote right, and I don't want to take the time to go find it): there are more things in heaven and earth than are dreamt of in your philosophy, Horatio.
Or, to paraphrase Douglas Adams: In an infinite universe, everything is possible.
These discussions came to mind while I was working on my own novel tonight and wrote the phrase I haven’t made up the reading I’ve missed nor gotten the class notes from anyone and realized it was the wrong language for my character. I've taken a lot of care to make it clear Matt is intelligent and observant. He has to be. He's carrying the observational weight of the entire novel. The reader has to trust his ability to tell the story and give valuable insight into his own character as well as those around him, otherwise the whole conceit of the novel collapses into the diary of a precocious fourteen year old. And that's not what I'm after.
I'm reminded of a friend who wrote a stunning first novel years ago with a very young narrator. She wrote a very smart scene early on where her narrator observed her mother walking through the grocery store, commenting not only on the height of her heels and the tightness of her shirt, but the reactions of the other customers in the store. Instinctively, my friend had done the work of getting the reader to trust this narrator's ability to reveal truth and tell the story even though she was ten years old.
So I don't think the question is one of whether a particular word or observation is believable. If the question of believability comes up, it's usually because the writer hasn't done the work to make the reader believe it.