Except he didn't refuse assistance.
The Chinese helped the Vietnamese train their military commanders; reorganize their defense and financial systems, including tax and fiscal policy; and create a solid economic base. They also helped the Vietnamese to mobilize the peasants to support war through land reform campaigns. Overall, there was a massive transfer of the Chinese experience of making revolution to the Vietnamese.
https://www.wilsoncenter.org/article/china-contributed-substantially-to-vietnam-war-victory-claims-scholar#:~:text=On the contrary%2C the Chinese,their war against the French.