Someone described it as a 'Freudian slip' which is 'an inadvertent mistake in speech or writing that is thought to reveal a person's unconscious motives, wishes, or attitudes'.
But I would give Ngeh the benefit of any doubt. Sometimes, we need to check in what language a person thinks. Very often, Malaysians think in their mother tongue or language first, then translate into English. A Cantonese is fond of saying, 'hei mou lei kum soh' ('he is not as stupid as you') or 'hei mou lei lum kum soh' ('he is not as stupid as you think'). In other words, he meant to say, 'They might think Indians are stupid, but they are not'.
I tried to find the post in Malaysia Chronicle by Dinesh, and if not mistaken, he took it as to imply 'so how stupid are the Indians?' See how easy it is to offend someone or race in Malaysia without even trying!