If Thailand adopts bitcoin as a means of payment, then they should not limit it to tourists only. Citizens should also be able to use bitcoin as a means of payment, so the policy may need to be reconsidered to find a better solution. It is very unwise to allow others to use bitcoin as a means of payment in their country, while their own citizens are prohibited.
I believe it's still in a trial phase anyway, so it's understandable if the users are limited[1]. Not to mention, the way it works is similar to how crypto credit/debit cards work, where merchants will receive fiat instead of crypto. It's no different than if you use the existing crypto card option and spend it, CMIIW. They promise more reformation, although most of them seem to be targeted toward investment instead of using crypto for payments, but who knows?
[1]
https://cointelegraph.com/news/thailand-tourists-crypto-credit-cards-regulatory-reform