When Moses and Aaron appeared before Pharaoh, they performed signs and predicted and performed plagues. Pharaoh's magicians, however, were able to mimic three of the initial signs and therefore explain away the signs as insignificant. Even if there are explanations for signs, whether in the exodus or hypothetical signs in modern day, this does not mean they are not legitimate.
[Aleksandr Sigalov:] This is why they are properly called "wonders" instead of "miracles" because all of the wonders God did in Mizraim were natural and scientifically explainable events. This is why scientists of Mizraim were able to replicate three of them. This is why perhaps the Hebrews did not believe Moses because they thought that he is just doing magic tricks, even though these were legitimate wonders of God.