In my home state of Minnesota in the United States, a common greeting when the mercury goes down below minus twenty Celsius is “Is it cold enough for you yet?”
Thailand is a different world, of course, but “Is it cold enough for you yet?” seems like a very appropriate greeting during the current “cold snap”.
"Cold" is relative. It depends on what you are used to and, importantly, how you are dressed. Even the two Russians at my condo were wearing sweaters last night.
While we wouldn’t call weather in the teens “cold,” it does seem “chilly,” especially since the wind is rather brisk. It is definitely more comfortable wearing a sweater or light jacket than a short-sleeve shirt.