Really, it's his fault for not believing that the gloom was a real thing. He didn't believe it — it sounded like complete nonsense to him, so he went along on this little trip just to confirm it. Unfortunately, it turned out to be very real. And though he tried to avoid engaging with the enemy, it's most likely that Ryan's presence attracted it. He's vulnerable to it. Not only is he quite the pessimist, he hasn't let anyone touch him beyond a handshake until just today.

"Oh, I wasn't looking to learn. It's just not something that would have been possible where I'm from, so I was curious." Ryan stops speaking briefly as he makes his way onto the boat, keeping an eye in Irisviel in case she tired herself out. After all, not only did she participate on combat, she healed a wound that likely would have been fatal and then patched people up afterward too.