How could anything similar to this happen?

[Tyiallyradil]

I am using FotE and Imperiales Œconomiæ mods.

I got the same offer in the early game from Armenia when we were in defensive alliance already.

No one can literally touch my mighty WRE ally, altough my eastern frontiers are being sacked and raided by the sassanids and their puppets

I couldn't accept that offer, but I took a 3000 gift instead.

So back to my original question, how could this happen?

[Aeratus]

Sure, AI has a habit of offering to become puppets actually. It's part of how it's programmed.

[shawn858]

That happened to me before. It's a smart idea on part of the AI. It stands a better chance of surviving with you by its side and it's practically reuniting the empire, so it's pretty neato

[Tyiallyradil]

How much does the AI have to like you in order to offer something like this?