It means it's nothing but a pitiful excuse for abysmal storytelling because one couldn't come up with a better reason. "Hey, it's magic, so there! Don't bother me with wanting to be able to actually follow the story..."
Oh, there has been much worse story-telling, trust me. Anyway, my point is you can't come up with ome sort of definitive answer to Vivec's moralities based on something you don't understand properly.
As for Sheogorath putting aside power to make it hit Vivec, I have some problems seeing him doing so after "Shivering Isles". The old Sheogorath isn't Sheogorath anymore, and the new one isn't the one behind the launch of the Rock, so why should he bother? Even IF he inherits some of Sheogorath's power at some point somehow, it would be hilariously "sheogorathy" for the new Sheogorath to get back at the old one for manipulating him by thwarting some of his actions.
By then Vivec had been taken by daedra, and the MoT was held up by the whatsitcalled seen in Infernal City. But then, it's not exactly easy for a standard mortal to freeze something in time and space,
and move it somewhere else.
Speaking of which, if the MoT is frozen in time and space, even Vivec wouldn't be able to move it, I'd think. He had stopped it from hitting Vivec by freezing it. This would stop ANY movement from happening, at all. Be it stopping it falling, or moving it elsewhere.
And I think that the fact that they hollowed it out was in fact, breaking existing lore. It shouldn't have been able to happen, but meh.
(by the way, I'm not arguing Vivec's morality, I'm neutral on the matter)