While it's probably not obvious because Newt is Newt, he's curious about Jean, too, since he comes from Armin's world. (And what he knows about said world is both fascinating and a bit horrifying to him.)

He's a little unsure about Jean because encouraging that behavior in a Mimikyu is no way to handle it getting upset at Pikachus!! But he also knows that sometimes you just can't help how a creature is. He seems nice enough, though there's something about him that gives off the vibe of some of the more..rough and tumble individuals Newt dealt with in school. (The people he tried to avoid because Newt + people in general is just not always a good mix.)

Still, any friend of Armin is someone he's willing to give the benefit of the doubt to!