What about it makes no sense? I find it to make the most sense, given it's about text generation and their models are named from shortest text to longest.

Well, they make sense, you are right, but it's not straightforward to match sizes to the length of each text.

They aren't, though- a fable is only bigger than a sonnet. Technically, an opus is any creative work, including a music score. A magnum opus would be a person's most celebrated work, but that doesn't have to mean biggest or longest.