Ignis grabbed Reno by the shoulder, seeing that he wanted to step forward. Since this is a memory, the guy can't do anything about it. Still- the way he says Ardyn's name-

"...you. You've met him before." It's more of a statement than a question. And you can bet your everything Ignis will want an explanation. The memory, however, is starting to blur and will eventually kick them out from it because they are conscious, but-! He needs to know!