Partly true. If I remember correctly, in that thread it was mentioned that new character classes created by mods would default to an always hostile AI, but @Ignasi has also mentioned it being an issue with the “hate list” unrelated to mods. I believe the latter is why the bearer in Sepermaru is hostile to the player.
By chance did you have a recently placed thrall with you? By recently, I mean since the newest update. For whatever reason, since the update it seems they run the risk of starting out with an “attack everything” stance. Access the behavior options from the radial menu and either select Guard Me or Attack Nothing. It’s worked for me so far to prevent that situation (when I remember to change it).
The Patch Archive is in a sticky thread.