Chambers, who has lived in Thailand for years, specializes in studying the influence of the Thai military, which plays a prominent role in the nation's politics.
This is the sole reason for the arrest. Besides, why are you arguing someone who has lived in a country for years is just a guest?
Not quite. Immigrants intend to stay forever, while expats don't (in my opinion).
That is, if these self-called "expats" do intend to stay forever and obtain citizenship they very much are immigrants who don't want to call themselves immigrants.