Sole Soryo ruler in 896 (no domain), I turn into Ritsuryo when I invade another ruler in Japan, is this a bug?

[Nettingman]

As the title says. I played one of the scenarios in 1066 first and I was able to conquer just fine. However now that I started in the 800s and I don't have a domain, whenever I win a war against a Ritsuryo ruler with 'Soryo county conquest' I get their title, meaning I become a governor. Is this a bug or am I missing something?