What is the ruling on saying "Allah did not say this" when witnessing an inappropriate act, and is this statement considered disbelief (kufr)?

Denying that Allah Almighty said something He did not say does not lead to disbelief (kufr). It is more appropriate to express it using the ruling of Sharia (forbidden, disliked) instead of "Allah did not say it," because the latter does not convey a ruling, as many permissible things have nothing specific said about them by Allah.