Do you never use any other languages in Thailand other than Thai?
I'm a Brit, when I'm talking with people I know we greet each other in all sorts of languages and ways.
I might decide I want to say Bonjour to people, or maybe greet them with 'Jo San' (Good morning in Cantonese).
I choose words I know my friends will understand. I studied French, Latin, Spanish and Ancient Greek at school and I have friends from more countries than I can remember, which means I've picked up a few words and even sentences in lots of languages.
Most of us know how to say hello etc in multiple languages, why do we have to limit ourselves to using our own language, or saying it in Thai if we speak to a Thai person? Why can't we say hello in French to a Thai person, or say hello in Italian, Chinese, German, Russian?
Regular Thais probably don't get enough exposure to lots of other languages, so they don't understand hello in multiple languages, but that is their problem not ours.