My question to the owner is, "so why didn't you call your previous contact person to get all the info you would need to cater these two events?" To purchase food with no mention of when 'next week' they want the food, or any details, doesn't make the business owner sound professional. Surely he has had people say, "we will use you for X" and then he never hears from them again?
Sounds like the owner got dollar signs in his eyes and bought the food with no further details. That is his problem, and no one elses.
Hearing of his story and his sign, I see his sign as a lie and himself as foolish.