It would tell him where the attack would come from though. The "speed demon" should have been able to dodge the bite. He shouldn't need to know what's gonna attack him, but simply where the attack will be coming from to distance himself from the trajectory of the attack closing in on him. Zoro was able to react to King's explosion despite having no clue what Jackpot even was, yet Sanji couldn't at least coat himself in Armament in reaction to whatever counter Nusjuro was gonna deliver? There's something sus with how Sanji handled this encounter.