Bless those two braincells for not having Inigo go loud in this instance. It wouldn't be the first time it's happened.

It's definitely a case that Tidus is hoping desperately against after saying the news, but after those first few seconds, Inigo's voice drops, and the relief is palpable. And it's rewarded by why a radio came up in the first place - so Inigo told them. He isn't sure if it's a good thing or not still (it's hard to tell anything, really), and the idea they took him because of what Inigo said...

"In that case, we might see Seto and Roland too. I... told them 'bout Halo." He tries to keep his voice particularly low. "That they met her. Didn't really want to let out too much, but... she's the only proof that the train's world existed, right? Her message."