Quran and grammar
There is no contradiction between Quran and Arabic grammar; firstly because Revelation of the Quraan was in a period where Arabic language have a high status between Arab tribes, and if there is one mistake they will not accept the message of Quran because they use to not respect those who made mistakes while speaking.
Secondly Quran have the same grammatical rules that Arabs used; for that it will comprehensible by theme.
Thirdly the grammatical rules as we know today appears in a later period when non-Arabs converted to Islam, and started to read Quran with grammatical mistakes; so that Arabic scholars started to make rules to prevent Arabic from change which can lead to misinterpretation of the Quran meanings.
So they started to write grammatical rules with the object to preserve the Quran, that's why they took almost of the rules from the divine scripture, and from Arabic poems, and Arabic normal speaking , with some strict norms.
Finally you can not say there is grammatical mistakes in Quran because, as said Dr Zakir Naik, the Quran is the textbook of Arabic grammar.
This is very interesting. I made a search about that and I found this
bear in mind that the Arabic grammar writen after Quraan so Yes, I think he is right