Exodus 8:5-8 The entire land was covered with frogs. This does not say the same thing happened with the magicians. It just says they made frogs come up out of the land. Was this demonic power, or just a great magic trick?
Here is what we know, that the land was covered with frogs from Aaron’s deed, and the magicians could not make the frogs go away.
Exodus 8:18-19 The fact that the magicians could not duplicate the gnats would make it appear that the previous deeds were tricks.