You are a tax resident of any country you spend more than ½ the year in... But that doesn't really mean anything other than you are supposed to file your primary taxes in your country of residence and possibly (like in case of USA) file taxes in your home country claiming any tax paid in your tax residence country as a tax credit on your home country taxes.
If you do it before July 1, then yes, if you reside in Thailand for the remainder of the year then technically that is money remitted into Thailand and could be taxable. Best to make your move here July 1 or after to avoid the 1st year of remittance.
Not everyone typecasts people. But fact is that many relationships between Thais and foreigners are in fact transactional. That doesn't take away from the relationship, it is just a cultural difference and acceptance and it doesn't apply to all. It's just one of many forms intercultural relationships can take.