Relative kind of knows the subject from Gai's babblings, and he wasn't exactly quiet about it to them. (And it would seem like he would be so excited about being a Ranger that he would probably babble about making them good guys or something like that.)

Which leads them to grab him and keep him until he stops having delusions of being a pirate, and also calling a random crewmember and telling them that he's not going to be a part of this and where they can find the Cellular.