you automatically become tax resident by residing for 180 days inside the Kingdom in a calendar year. You absolutely become tax resident at a certain moment, the moment you reside 180 days within a calendar year. This is not a difficult concept to grasp.
to pay Tax in Thailand you must be tax resident and have assessable income. Assessable income includes foreign sourced remitted income and not just domestic income.
spending 180 days inside the Kingdom in a calendar year means you are Thai tax resident. Being a Thai tax resident and having to pay Thai tax are two completely different scenarios.
not quite accurate. You can legally be Thai tax resident and never have a Thai tax filing requirement. Tax residency just means you are subject to Thai tax law.