Slitherine

I'm playing a game as Persia with the new DLC, and at some point I get a message that Athens becomes a client state. This completes the Persian mission for the conquest of Greece, though at the time I wasn't at war with Athens or any other Greek state, and indeed no Persian had set foot in Greece. I played a Hellenes interloper decision on Athens in a previous turn, so it might be because of that, but I don't feel like I really earned the completion of the Greece mission. Is it really a good idea to allow client states to be made with regional decisions (assuming it's due to that), especially since AI client states never betray their overlord?

That's not related to Hellenes interloper, this is related to Athens being besieged by Sparta (or another Greek nation) and in the process of losing the capital. In a last minute move, they prefer to bow before mighty Persia ...

Thank you for the clarification. It appears Athens was indeed being besieged by Sparta.