No, you are not Sabbat, but one of the NPCs is former Sabbat, which may have given you that impression. One of the NPCs is a rather high Humanity Anarch and the rest are Camarilla.
I believe you killed the [[Spoiler]], which is why you got the ending screen. It would be fair to say the ending was too abrupt and I'll make sure to take that into consideration in the future. Thank you for playing!