You're right. Taken at face value, you could e.g. enroll into a Muay Thai class in Thailand, get the required paperwork from the school and go to a nearby Thai embassy or consulate such as Vientiane to apply for the DTV in the "Thai soft power" category without having to return to your country of residence. Super convenient for many if that turns out to be the case.
But I'm wondering how much scrutiny, if any, foreign bank statements will attract. There's no easy way for the RTE Vientiane to verify them. Not a big deal when someone has to show having 20,000 baht for a tourist visa, but I'd imagine they might care a bit more if a DTV applicant actually has those 500,000 baht that are required.