Thailand is known for its tourism, and it is true that some foreigners live in their exploding tax loopholes. But this policy can create a negative impact on foreign investment and tourism. Many foreigners were happy about their low tax rates, which made them an attractive place for many expats. Most of these expats were already paying tax in their home country; now if they need to pay a high tax in Thailand as well, this will force them to leave the country.
I don't think that they are including tourists on that law so I don't think the tourists need to worry about that, they're probably talking about expatriates who have been living in Thailand but are working in overseas and are getting paid by the country that they're working from so if you're a tourist nothing to worry about I think. I think leaving the country for some of these expatriates are far fetch thing for them to do because what's a little more tax compared to going back to their country with a much higher standard of living than what they currently have in Thailand.