The Shaykh’s explanation of the doubt that caused this distinction between ahad and mutawatir.

The Shaykh : A doubt was presented to them, and over time it became a belief for them, namely that an ahad hadith does not convey anything but conjecture, and by conjecture they mean the predominant conjecture, of course, and...
If we were to grant them this claim in its absolute form, we would ask them: from where do you derive this distinction? And what is the evidence for it from the Book and the Sunnah? They claim that it is obligatory to act upon ahad hadiths in matters of rulings, but it is not permissible to act upon them in matters of creed. We have seen some contemporary scholars cite as evidence for this the saying of Allah the Exalted in...
...and He rebuked the polytheists for adopting conjecture and following it. These people, citing these verses as evidence, state that the rejected conjecture in these verses does not refer to the predominant conjecture that is conveyed by an ahad report and upon which it is agreed that one must act, but rather it refers to doubt, which is the... It was stated in Al-Nihayah fi Gharib al-Hadith and Al-Lisan and other books of language, the text of which is: "Conjecture is doubt that arises in you regarding a thing, so you verify it and judge by it". End of quote.
This is the conjecture that Allah the Exalted rebuked the polytheists for. Supporting this is His saying about them: Thus, He made conjecture to be a mixture, which is mere guessing and estimation.