You have been identified as someone trying to stay long term in Thailand on tourist entries. That is in the computer system now. Remember that buying a tourist visa instead of using a visa exempt entry does not guarantee you will be let into the country. Chances are very good that if you try to enter again as a tourist, whether you buy a 60 day tourist visa, or not, you will be refused entry. They warned you, and their computer system is excellent.
Currently there are no requirements that you even attend the courses you signed up for. This will change in the future, as the abuse is identified, but it won't affect you for five years, unless you decide to extend the 180 day entry inside Thailand.
If you extend it inside Thailand you will need to provide all the original documents you used to get it, and they need to be updated, including your courses.
Three months minimum as of now, and as more abuse is recognized it will progress to 6 months minimum in the near future, as has happened at other Thai embassies/consulates. The required times change monthly.
Padkrapow4549 you may not like it, but they change things as they see how they are being abused. Had the other person you referenced already been taking Muay Thai classes, and not brand new at it? Everyone uses the same embassy in Vietnam for Muay Thai classes, so that embassy sees what is going on. There are some "reputable" gyms that have more people signed up for classes than their gym can handle...lolol