The landlady had said exactly the same to the birthday girl who had arrived early. So it wasn't about being late
No, it was about MANAGING EXPECTATIONS.
The manager was EXPLAINING TO YOUR FRIEND that she did not have exclusive use of the table for an indefinite period of time.
RESTAURANTS ARE THERE TO MAKE MONEY, and the only way they can make money is by SERVING A CERTAIN NUMBER OF CUSTOMERS EVERY SERVICE.
Customers need to SIT AT A TABLE in order to eat their food.
Restaurants have FINITE NUMBERS OF TABLES.
As you may be aware, there is a TEMPORAL DIMENSION TO THE WORLD AS WE KNOW IT - in other words, TIME IS A THING THAT EXISTS.
Therefore, most restaurants seek to "turn tables" during a service, ie have MORE THAN ONE SEATING ON EACH TABLE. Your party was the EARLY BOOKING.
Clearly, there was a LATE BOOKING on that table too.
Your party NEEDED TO HAVE VACATED THE TABLE BEFORE THE SUBSEQUENT PARTY ARRIVED, so that the new arrivals had a place to sit down.
This means that you needed to have ordered, received your food, eaten it, asked for the bill, argued over the bill, and paid the bill, BEFORE THE NEXT PARTY ARRIVED.
Customers have the use of their table for a finite but reasonable period of time. If they CANNOT BE FUCKING BOTHERED TO ROCK UP ON TIME, then it is impossible for the restaurant to serve them in the anticipated timeframe.
Informing customers that they have the use of the table for a finite period of time is normal practice. The manageress was not being a bitch. She was trying to explain a really fucking basic concept. I can only imagine how she must have gone into the kitchen and howled with laughter when you stormed off, affronted by her temerity.