On twitter, I saw a bit of praise for Thailand's 'young' team, that rather ignored the fact that this was also a young, somewhat experimental NZ squad.
I also got the feeling that (on here), there was a bit of under-estimation of the Thai side. Understandable, given the shambles the national team have been recently.
However, the U23s have been in regular camps (a couple of days a month) all year long, as for some reason, the FAT put all its focus on the Asian Games (an Asia-only Olympics). The U23s benefited from a proper build-up, complete with friendlies, and made the semi-finals before losing to South Korea, and then Iran to finish 4th.
While the senior side hadn't had a coach since March, and sent a joke of a side to China in October, the promotion of U23 coach Kiattisak Senamuang meant they were always going to be a different kettle of fish last night. Part of Thailand's 'Dream Team' in the late 90s, 'Zico' has the respect of the current generation. Also, this squad was heavily based around the players he's been grooming for the past year. Despite injuries to key midfielders Adul & Chappuis, he was able to replace them with players who recently played a month-long international competition. He'd also had this squad training for the last 2 weeks.
What you had was a Thai team that had, for the most part had regular training camps with their coach all year, and were familiar with his tactics. They have also come off a full season, which included a tough international competition, compared to a New Zealand team that had been together for just over a week, and are still getting to know what's expected from a coach who's in his 3rd game in charge.