That is not true
That is only internal damage, as they bypass skin but Zoro cuts so deep he doesn't need to by pass skin.
Have you not seen people cough up blood before time skip?? Why do you think it happens?
Reason why Luffy learned internal destruction is because his Haki isn't strong enough to do real damage to Kaido by attacking him on skin.
Zoro doesn't need that.
It isn't some deep shit, it is the most obvious thing ever