yes this is the current situation and thailand may only tax money remitted to thailand. it is proposed that they will tax globally like many other countries already do. i think it is unlikely but it is being talked about now and may happen.
by global tax we mean that thailand may tax any overseas income in the future, rather than thai income or income remitted to thailand which is what it is now.
uk investments for non-uk tax residents are not taxed so many wont have tax paid. in this case the CG would be taxable if remitted to thailand. agree unlikely to get caught but also dont want the possibility. i plan to be non thai resident every few years and transfer a few years living expenses from uk in that year. take a 6 month holiday from thailand every few years....
i have an account there but not transfered yet, but as far as i know as a non-uk resident (based on days with the SRT) my uk investments are not taxable (unless its property)
property is different in the uk and taxable for non residents, but dividends, or cgt from selling stock etc is not taxable for non-residents as far as i know (and have called hmrc twice recently to confirm thsi)