The words for rambutan and idiot are nothing alike.
Different tones, different vowels, different vowel lengths.
The danger transliteration.
It's like in English, maybe:
Cough and Rough look like the same vowel sound but one is 'off' and one is 'uff'.
In fact, you can pronounce 'ough' 9 ways.
You saying ngo is like ngaw is like a Thai saying
A ruff, duff-faced pluffman strode thruff the streets of Scarbruff after falling in a sluff, he cuffed and hiccuffed.
A rough, dough-faced, thoughtful ploughman strode through the streets of Scarborough; after falling into a slough, he coughed and hiccoughed.