Ryujin
Legend
I'd guess that your player is confused by the Double Move rules (PHB 284). That's the only place I can think of where you can add two Move Actions to get something else (or any other adding of two actions to get something else).
But regardless of where the error comes from, it's an error. There's no rule that lets you trade up lesser actions into bigger actions.
Even that doesn't make any sense because when you "double move", you move twice as far. There really isn't a whole lot that's funky about it.