It's either treason or it's a felony under the Logan Act. Not both.

Unauthorized negotiation with a foreign government is a violation of the Logan Act.

Overt acts (including unauthorized negotiations) which provide aid and comfort to enemies of the United States are treason.

The two categories are basically orthogonal; they aren't mutually exclusive.

I think that it could be a treasonous action, but also not literally meeting the terms of treason as set out in law.

In other words, it could meet the common-person interpretation of the word, but not the legal offense.

How is notifying the Iranian government that Obama doesn't have the power to make any deal without their approval a violation of the Logan act?