For Vassal% would getting accepted to take up a claimants cause count as vassalization?

I want to say yes, because you've sworn fealty to them even if they aren't technically the king/queen of a faction yet. But then I also think, why would you bother going for them in vassal%? Since the renown you need to take up their cause is higher then the renown needed to swear fealty to a faction leader. 200 compared to 150 which can also be effected by your relation with them.

I was just wondering