This is because most mini splits are meant for a global audience
One of the quirky things about mini-split air conditioners is that they are basically the air conditioner of choice if you want central air conditioning outside of North American and the existing installed base in places like Europe and Australia. North American-style split systems simply aren't used in the rest of the world, for a variety of reasons that have largely to do with space and efficiency, and as thus, mini-split manuals are written for a global audience, not a US one, even when written in English by major global manufacturers who are used to selling to North America (such as Mitsubishi).
One artefact of this is that they often specify cables in a way that's only crudely translated to US nomenclature. Most of the time in the rest of the world, something akin to a tray cable is used, and in tray cable nomenclature, the green wire is counted among the wires of the cable, as it may or may not be necessary as an equipment grounding conductor, depending on the application of the tray cable. However, Exposed Rating/Joist Pull rated tray cables (designated TC-ER-JP), the only ones that can legally be used without conduit in a dwelling unit application under the NEC (as per NEC 336.10 point 9), are thin on the ground from what I can tell; many HVAC sellers will try to sell you tray cable as "mini-split cable", but it's not appropriate for the application.
So, I'd run individual 14AWG THHNs (black, black, red) up the flex whip to the disconnect box, then tie them into 14/3 W/G NM at the AC disconnect with black and a remarked white for the hot wires in the NM cable, red for the comms wire, and the ground of course tied to the disconnect's ground terminal. Then, this 14/3 W/G NM can be run to the indoor unit, just like you would run any other mains circuit. (Of course, if you're under codes that prohibit NM, you can substitute a MC or AC cable instead, or individual 14AWG THHN wires in metal conduit for that matter.)