That is ignorant talk. If you have your nation's DL (with motorcycle) and the IDP (and you stay under 90 days), you do not have to pay any fine. Before I did my Thai motorcycle DL I was stopped several times with my foreign DL and IDP without any issues.
You ask this anonymously, because you know the answer, already, right? 🙄
With the DTV visa (DN path) you are allowed to work for a foreign company and in work fields outside of Thailand. It gives you a permit for remote work only. You are not allowed to work with customers in Thailand.