↑ Quick pic of battle stances in Hakuouki.
Every ryuha has its own style in fighting, and even style of life. (Kendo is more than just a fighting skill.) A learned swordsman can tell which ryuha his opponent came from by crossing swords.
However, before Hijikata settled down in Shieikan, he roamed Tama area,
picking fights learning from dojo here and there. His mixed fighting style was unique, hence it’s perfectly normal for his style to be different from Okita’s.
I believe Hakuouki put quite some efforts into designing fighting styles. The battle stances are real. And those from the same ryuha use similar stance.