Well thats Thailand protecting it's tourism. Gnadenburg, You and your daughter were very lucky.
The chances of getting stung by a box Jellyfish are low I believe. There have been some recent deaths in the last couple of years from Box Jellyfish and they are not really doing much to bring attention to the issue. But there have been deaths on both the east and west coast of Thailand. Although I wouldn't let this discourage anyone from traveling to the region and there is a much greater chance of getting killed in a motorbike accident while on vacation in Thailand.