At first Lucas is kind of confused as to how this supposedly-large creature can fit inside a small plastic ball. As it grows... okay he's still pretty confused, but maybe it's best not to question things from other worlds too much. He might have asked about it before he was distracted by the appearance of a large orange dragon hovering in the sky ahead of them.

That... did that seriously just come out of a ball??

"Wow, he's big! He can fly too?" The Pokemon looks friendly enough though, and if something like the menacing looking Drago can be friendly, he's sure this was no different. "Um, hi Dragonite!" Hopefully he can understand him!