The Logan Act is a federal law that "criminalizes negotiation by unauthorized American citizens with foreign governments having a dispute with the United States."
So it depends how you define negotiation and unauthorized in this context.
It's a violation of the Logan Act if you: a) consider the conversation a negotiation, and b) consider Flynn an unauthorized representative at the time of the call
The Logan Act is a federal law that "criminalizes negotiation by unauthorized American citizens with foreign governments having a dispute with the United States."
So it depends how you define negotiation and unauthorized in this context.