Hey, there's nothing sad about that. They might have found it troublesome to make the whole episode some gala with everybody attending in suits and dresses like that. Thus, the only way to give us joyous images like that (kind of fanservice) was to have them as nonsensical background for the credits.

There's only so much you can tell in 30 mins, as an independent story especially with lots of characters, which I believe was probably a studio requirement for this kind of Jump Fest extra. Considering that, considering this was equivalent to fillers, I say this was a masterpiece.