At the time of the filming, they don't know who will be their plus-one guest, hence they were surprised to see Shun joining them.
Jun: Honestly, I somewhat predicted it...
Jun: He might be coming in time for Gaku's promotions...
Shun: *smirk*
Shun: Yes. Today, I came for that. *smiles*
He seems to keep tab on each of his friends' upcoming movie releases. How about the other one? LOL
P.S. For a split-second, I saw Masami's face in VS Arashi. Miracle. LOL