That article just confuses me. It says it is ok and then contradicts it a paragraph later. Eg:
"Digital nomads – people working remotely or running online businesses – in Thailand can legally work there on tourist visas"
But one paragraph down:
"It is unlikely that travellers will be granted a re-entry stamp after two or three visa runs. If your passport is stamped “O-I” (out-in) upon arrival, it is unlikely that you will be able to re-enter the country again should you decide to do a visa run"
It is confusing two separate ideas. One is that it is ok to work while on a tourist visa, the other is that doing multiple visa runs (regardless of whether you work) is not ok. The out-in problem is true of many countries and has nothing to do with working.
"Digital nomads – people working remotely or running online businesses – in Thailand can legally work there on tourist visas"
But one paragraph down:
"It is unlikely that travellers will be granted a re-entry stamp after two or three visa runs. If your passport is stamped “O-I” (out-in) upon arrival, it is unlikely that you will be able to re-enter the country again should you decide to do a visa run"