That is ... something. He hasn't experienced a disappearance quite as directly himself - luckily - but when Sasha went missing, it had only been something like two days after Cooper last saw him. And that had been a bit of a shock, so ... he thinks he can understand her.

"The worst part is knowing how unlikely you are to see them again."

That's just the thing about the different worlds aspect in Johto, isn't it?

If it sounds a little like he's thinking out loud when he says it, it's because he is.