That is not how the concept of "Trinity" came about. But we can't blame him because many Christians are also not sure about this.
Nonetheless, we expect Naik to at least demonstrate some knowledge based on doctrinal research about the core belief of Christianity, as he is noted to be an expert in comparative religions and the President of Islamic "Research" Foundation.
Although many may find it daunting to learn about Trinity, there are accessible resources available for the task.
Stephen Holmes's The Quest for the Trinity: The Doctrine of God in Scripture, History, and Modernity published in 2012 by IVP Academic is one such resource. Holmes is a theologian at University of St. Andrews, Scotland.
The book gives wide overview of the important debate within Christianity about the doctrine. It tells us how the doctrine arises largely as a response to the "exegetical pressure" of various verses in the Bible (p.53-54: 1 Cor 8:6, Matt 28:19, 1 Cor 12:4-6, 2 Cor 13:13, Gal 4:6, Eph 4:4-6, Rev 1:4-5).
Holmes shows us that the concept of Trinity is still very much debated even among Christians. In the first chapter, Holmes summarizes all the big ideas among the great twentieth century theologians, namely Karl Barth, Karl Rahner, John Zizioulous, Wolfhart Pannenberg, Jurgen Moltmann, Robert Jenson, Leonardo Boff, Miroslav Volf, Cornelius Plantiga, Richard Swinburne, Michael Rea, and Brian Leftow.
Thus, it should not surprise Christians that non-Christians express doubt over Trinity. But that is not the point.
The point is a heuristic one: If Christian theologians are still debating about the Trinity, then anyone interested in comparative religions should ask, how did this whole debate come about, especially when the word Trinity is not in the Bible?
The concept of Trinity is one of much nuance that non-experts may find fumbling when learning about it. Take for instance, this sentence in the book:
"Barth's denial of a Logos asarkos, Rahner's insistence on the identity of the immanent Trinity with the economic Trinity, and Pannenberg's and Moltmann's desire to see God's life as open to the gospel history, all reach their most extreme, and most coherent, expression in Jenson's theology." (p.24)
Thus, Christians must learn about their core belief as much as non-Christians who are expert in comparative religions should.
Inter-faith dialogue and understanding in the world, not only in Malaysia, deserves better experts whose working knowledge is based on real research on theology.