Of course you know very little and what little you know you do not know their proper context in history.
Upon the surrender of a hostile but defeated power, territories conquered by said defeated power must have their administrations transferred over the victorious power. The accepted protocol is that duly appointed agents of the victor must appear in person to accept that transfer of authority and control. Upon said acceptance, the military units of the defeated power then are nominally under the authority of the agents of the victor. Imperial Japanese troops in Indochina did not give up their weapons but instead were ordered by the Allies to keep their arms and to retain their authority to maintain order until Allies officials arrive. Nationalist Chinese were such appointed agents for northern Indochina with northern Viet Nam their first contact.
So of course Chiang Kai-shek's original intention was never to have China be a permanent custodian for Viet Nam. He, Stalin, and Roosevelt already came to an agreement that Indochina was to be under UN administration towards full independence. Keywords search for the clueless Chinese: 'indochina un trusteeship'.
Yeah...Thanks to the Viet Minh who invited France back in again...Another clue for the clueless Chinese...
Ho
Note the date and see how soon that was after WW II. Chinese troops were still northern Viet Nam at that time. Even without said agreement between France and the Viet Minh, colonialism was over. France would not have lasted long no matter what. The viet Minh then used French troops and weapons to slaughter non-communist allied Viet nationalists. Then the Viet Minh turned against the French with Mao's support and insistence that China must have a communist buffer. It was only when communist China got fully involved that the US had to nominally 'support' France as an ally against communism in Asia.
So we can say that China was a co-starter of the Vietnam War.