If I remember correctly, the USSR was Vietnam’s chief backer. These countries prefer the big boy from far away rather than the one on their doorstep. For the same reason Albania cultivated the Chinese. This would explain part of his attitude toward Russia.
Both but USSR more after late1968
http://alphahistory.com/vietnamwar/chinese-and-soviet-involvement/
When McCain was captured there were 170k Chinese troops still in Vietnam