Actually, if the cancelling is not intentional (in other words: a bug), and you are using it to your advantage (in other words: exploiting), there is absolutely no difference between the two.
That said, there are huge differences regarding the impact of bugs like that, and there are also bugs that are too easy to accidentally reproduce, that it's more or less impossible for Riot to ban people for abusing it.
That's why there's not 100% consistent ruling regarding exploits. But all that means is that any intentional exploit of a bug can potentially be punished by a permaban, depending on the obviousness of the intent and the impact of the bug.
The bug Lee Sin's E had, when he was first released was probably one of the most extreme cases. It was so easy to reproduce accidentally that Riot couldn't ban anybody for it, but so impactful and widespread at the same time, that Riot actually had to compensate Lee Sin balancewise, when they removed it.
Edit: In this case, btw, I'd argue it's rather difficult to ban for it, since it's the Tresh that gains advantage, but it can be triggered by the person taking the lantern. If you can read Thresh players you might otherwise be able to intentionally try and get Threshs banned for exploiting a bug they might not even have known about.