「作法が厳しい、貴族向けの高級な店だ」と都合よく勘違いしたから

Every time they opened a door, a mysterious order was written. 'Please comb your hair neatly.' 'Please brush the mud off your shoes.' 'Please leave all metal objects, especially guns, here.' The two misunderstood, thinking 'It's a restaurant with strict etiquette; there must be many noble guests,' and kept obeying the instructions.