As for why he mobilized troops and issued orders on his own authority without reporting to the Royal City, that was also understandable.
If the Royal City had known that Cao Can was doing such a thing, they definitely would have refused. Even if the Royal City shared the same concerns, before a complete break with the State of Qin, they could never have agreed to such actions.
Now that Cao Can's troop mobilization was unauthorized, should the State of Qin hold them accountable, the Royal City could simply claim ignorance, asserting that it was the work of a subordinate commander acting on his own. At that point, they would only need to give Cao Can a slap on the wrist by transferring him away from the Hetao region.
Chapter 934