I mean, they made Orion look bigger than Starship, so maybe don’t assume everything precisely is to scale.

That being said, if the depot has no “payload” other than the bare propellant tanks, with no heatshield, no flaps, and no header tanks, I wonder how much they could stretch a Starship. Since the depot is to be filled by tanker Starships, it wouldn’t even need to make it to orbit with any propellant to spare, since it can just be refilled later.