As others have already said, this is terrible advice.

I also think the tone thing is overblown. Even in English, there are lots of words that have different meanings but are pronounced identically: consider ware, wear, where. How do you tell them apart? With context: only one word fits into "Ware/wear/where is the shop?" or "I ware/wear/where clothes".

The same goes for Thai: a request for a monosyllabic khao will cause puzzled expressions, but asking for khao suay ('beautiful rice' = plain rice) will easily get the message across. If you're giving a cab driver instructions, he'll be able to distinguish between trong pai (keep going), liaw sai (turn left) and liaw khwaa (turn right) even if your tones are all over the place.