When he asked you what you're doing and heard the word seminar he definitely thought you were working illegally. Probably safer to say learning to cook or Muay Thai.
It seems they don't like it that you spent time in Thailand previously and applied from a neighbouring country. They think some people have been working illegally in Thailand.
Exactly. The only people who should be "hoping for more scrutiny" are Elite visa holders. And certainty not fellow DTV holders who for some strange reason think theirs is superior.
If on soft power they will look you up and down. Learning to cook = overweight. Muay Thai = lean. Dental = swollen mouth. If you don't match they will question you further.