People commenting here on weight issues may not be familiar with Thailand and weight discrimination. They hugely discriminate against over weight people. In fact they mock them sometimes by asking if you are pregnant and that sort of comments. So I do understand what the three passengers have gone thru.
Furthermore there is no information on what airline and what class they flew into Thailand. This would probably give a better picture of the situation.
As for safety it's interesting that some are saying that belt extension can be fitted on the 787 but TG may not have the capacity. They didn't handle it well of course. They should have taken into consideration what happened at check in and refunded them the full amount for the sake of good customer service. Knowing how inept the management is, this is what I would expect from TG.