There's a moment of guilt followed by a burst of anger. It's not directed at Prompto. It's just this entire situation is--frustrating. And in the next moment, it dies away, the emotion spent. He's simply too tired to even keep it going.

Ignis might not have his sight anymore, but he knows some of it is Prompto needing to help. To do something. All nervous energy without an outlet, like a puppy. Noctis isn't up to hanging out, they're standing still in one place, and there's a very limited set of what Prompto and him can do.

"... and perhaps afterwards, we can take a walk."

Well, if it works for dogs....