There's a reason much of the older generation of Viet military and political leadership studied in Czechoslovakia, Poland, East Germany, BSSR, and RSFSR and why both the Vietnamese Army and the MPS still send their officers and leadership track personnel to train in Belarus and Russia to this day.
Heck, Russian is still an fairly popular language choice for Viet students targeting civil service or police careers.
Furthermore, a ragtag army of farmers would not have been able to fight against the PLA in 1979 or overthrow the PRC's lackeys and backed by the US in Cambodia and Laos in the 1980s-1990s.
It's also why you find so many Vietnamese in Prague, Warsaw, East Germany, Minsk, and Moscow to this day.
The fiction of "illiterate paddy farmers pushed American soldiers out" is just a salve around the reality that the US abandoned South Vietnam in order to seal the US-China deal in the early 70s that helped contain the USSR in the late 20th century.