Nothing is written about taxes. So you will be a tax resident.
It makes a lot of sense to ask first what you work, then give you a visa and then tax you.
Much better for Thailand than the way it's now: you come here anyway, under all kinds of visa, nobody knows that/what you work, you don't pay taxes here.
BTW these are taxes for Thai-sourced income, DTA won't help. You can claim a tax credit in your home country if you pay taxes there, too.