I wouldn't get too wrapped up in this "fact".
It appears the Khmer Rouge (Cambodian Communist Party) was in existence prior to 1970. However, it was not a significant factor until starting around March, 1970, as it had fewer than 3,000 members before this.
The following is from the Encyclopedia:
(Pol Pot) was born in Prek Sbauv in what was then a part of French Indochina... In 1949, he won a scholarship to study radio engineering in Paris. During his study, he became a communist, and joined an emergent Khmer communist group. This group was called the French Communist Party. In 1953, he returned to Cambodia... In the late 1960s, Sihanouk's head of internal security, Lon Nol took brutal action against the revolutionaries, known as Khmer Rouge. Pol Pot started an armed uprising against the government, supported by the People's Republic of China (PRC). Prior to 1970, the Khmer Rouge was an insignificant factor in Cambodian politics...
http://united-states.asinah.net/american-encyclopedia/wikipedia/p/po/pol_pot.html
The formation of the Khmer Rouge is murky, but it was apparently an established movement in 1968. However, as the NVA totally controlled the Cambodian border areas at this time (and there was very little Cambodian population living there) it is unlikely there were many, if any, Khmer Rouge in this border area (5 miles across the border?) in 1968. It was not until a couple years later they really got established as a military force.
... unfortunately, still too late for John F. (Fraud) Kerry's fanciful story....
Bottom line: regarding this latest BS from Kerry,
Kerry wasn't in Cambodia(which is what we're trying to prove from his latest lies) and Nixon wasn't POTUS in 1968 as Kerry was trying to foot the blame for the war and his presence there on!