The caller, Worapoj Pluksacheep, 20, told police he was sitting in a sala at the entrance with a friend when they noticed a bag tucked under one of the seats.
Fearing it might contain a bomb, he called the police.
The EOD officers spent 15 minutes gingerly checking and then opening the bag to reveal its contents about 10 kilos of kapi – shrimp paste.
Mr Worapoj was thanked for his alertness and civic-mindedness. The bag was taken to Muang Police Station to await collection by its owner who will, presumably, be rather embarrassed.