The term 3rd World Country refers to the unaligned countries of cold war. Yes, many of them were poor countries, but some weren’t. As the cold war is over, there are no 1st world, 2nd world or 3rd world countries any more and so Thailand is not a 3rd world country.
Maybe in your ignorance and tendency to watch US media you actually meant developing country.
Developing status for a country refers to the overall level of development of a country, and while Thailand does some high end manufacturing the economy is still far for developed over all
Plus, developing nation status is something a country can apply to itself, which gives them advantages in international trade based on WTO rules
But Thailand scores very high on the Human Development Index, so all of these things depend on the categorisation scheme.