All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, we would like to mention that a Muslim should avoid discussing with the people of falsehood if he does not have enough knowledge to refute their misconceptions so that these misconceptions would not affect his heart and spoil his religion.
Of course we are very concerned that the truth is clarified to a non-Muslim so that he would be convinced with it, but it is even more important for us to clarify the answer to you so that you will benefit from it.
In answering the question, we would first say that it is Allaah Who revealed the Quran and Who challenged with its eloquence the Arabs who were the speakers of this language to bring a Chapter like it and they were unable to do so. Had they found any defect in its eloquence, they would have declared it. Secondly, some scholars stated that the verse is assumed to mean: O people say: Al-hamdu lillaahi Rabbil-‘Aalameen. Such assumption is common in the language of the Arabs in which the Quran was revealed and in which the Quran is understood. This is confirmed by the fact that the Quran was revealed in principle in order for the believers to worship Allaah by reciting it; Allaah Says (what means): {And recite, [O Muhammad ], what has been revealed to you of the Book of your Lord.}[Quran 18:27]
Allaah Knows best.