Eh, he's an assassin in the way that
and
can be. They can go in and murder someone suddenly(they have the assassinate part down), but their only reliable option for getting out is to run(their escape plans are crap compared to the rest of the assassins, I guess Noc can launch his q, so he has a "run faster" option?).
And by the their definition, an assassin has ways to get in, do burst damage, and get out with their mobility spells. A diver has ways to get in, usually does a burst of damage, then either has to stay there and continues brawling with their auto attacks, or run on foot because they lack an escape that is not flash. In the "campion subclass" list, some found it weird that Noc was put in with the assassins but Rengar was not.