Looks like those who guessed (me included—but I didn't state it out loud) that they were an adventurer couple are correct, but the cause of the attack surprised me.
Dinoso's hinting that he's "the person of the Luffe" concerns me, however.
Is he hinting to Jean that his attempt at cover was useless afterall? And that the adventurer's guild, with its network of informants knew it was Jean all along? But that out of respect for him and his unknown powers, they stayed silent and did nothing of it. Afterall, Jean's not doing them any harm, at least for now—so better keep him friendly.