I used to work at a Haitian restaurant. And I can atest, that maybe it WAS busy before you get there. Black restaurants(Caribbean restaurants in particular) get VERY sporadic business, which often causes staffing problems because the owners don't know if they should higher more folks and risk being overstaffed and losing money, or to only keep 1 or 2 employees on deck and risk getting swamped with customers and not enough workers. We used to experience the same problem, where one customer would call in for patties(and we'd frequently run out too) and when they got to the restaurant either the patties weren't ready, or the sole worker/waiter/greeter/bartender on staff(me) really WAS swamped with customers by the time the angry call-in customer arrived. Often times customers would come in and be like "It's not even busy, why couldn't you do XYZ" but usually it really WAS busy 30mins prior to your arrival, and it died down as soon as you got there.
When you're the sole waiter/bartender/greeter on the floor(like I was often times), and you gotta serve 3 or more tables AND you gotta take call-in orders, it can make a seemingly simple job 10 times more difficult. Not to mention that these restaurants have so much employee turnover. So one minute a waiter might have help on staff, and the next second that worker quits and you're back to being by yourself. It's tough. It isn't McDonalds or a major corporation, finding staff is TOUGH. It's a guessing game week to week on how many customers you'll get. So you either end up with 3 waiters and a slow week, or you end up with one waiter and a CRAZY week. I've seen it all working at a Haitian restaurant for a year. One day I had to serve 7 tables by myself, and mix the alcoholic beverages for the patrons at the various tables, all-the-while answer the phone to take to-go orders, all the while taking walk-in to-go orders. Let's just say the customers were PISSED at me and many of them left. But I couldn't even blame my boss, because prior to that hour the restaurant was completely EMPTY. And the week prior was slow.