That is really poor reasoning and reminds me of the arguments of some Christians that dinosaur bones and other evidence pointing to the earth being billions of years old, were made by Satan to deceive us.
Truth is truth and all truth comes from God who is a God of Truth. Whatever is true is from him. If extraterrestrials exist and come to earth, irrefutably proving their existence; then their reality originates from God, not Satan.
Heck, Satan’s power is overrated - he can’t create a single tangible proof on earth that disproves God’s existence. Why assume he can elsewhere?
If you think satans power is overrated than you too have been deceived.
Even his buddy has the power to call down fire from the sky.
Rev 13:13
And he performed great and miraculous signs, even causing fire to come down from heaven to earth in full view of men.