Yes, because Flynn couldn't have done something shady outside of the calls the FBI reviewed.
Maybe an example can illustrate this more clearly for you. A dude is suspecting of kidnapping, the police search the house and find no one. Then a month later, the dude confesses he had kidnapped someone. How is this possible?
Because the kidnapper didn't keep the hostage in the house.
"I had to fire General Flynn because he lied to the Vice President and the FBI. He has pled guilty to those lies. It is a shame because his actions during the transition were lawful. There was nothing to hide!" - Trump via Twitter 12/02/2017