You're projecting (unconsciously/consciously taking unwanted emotions or traits you don't like and attributing them to someone else).
You feel that Thai people have got it in for us foreigners so you find things that back this emotion up. As has been pointed out to you by several posters, the person in question could simply be doing this for everyone (Thai and foreigner alike), but you see this simple act of neccessary protection as only be aimed at foreigners.
You need to be less sensitive.