I suspect that the program reasons like this. (And that it is a bug)
1) China should control the partisan in French Indo-China.
2) All Chinese partisans are Communist.
3) The Chinese Communists are controlled by USSR
4) Hence the partisan in Indo-China is controlled by USSR.
However, this reasoning is flawed. The main reason, in my humble opinion, is that the rules does not state that all Chinese controlled partisans are Communist. It states that partisans in China are, but this partisan is not in China and therefore the rule does not apply. The partisan should be controlled by the Nationalist Chinese.
RAC: 13.1 Partisans (option 46)
....
Controlling partisans
Partisans in ‘green’ countries are controlled by the major power that controlled their country before it was
conquered (or still control it if it isn’t yet conquered). Partisans in China are always communist Chinese units.
French partisans are controlled by the Free French unless it is completely conquered, after which they are controlled
by the Soviets.
Partisans in ‘red’ countries are controlled by the nearest major power currently at war with the major power
that controls the country. The nearest is the major power whose capital city is closest to the minor’s capital city. If
no major powers are at war with the controlling major power, then the nearest major power on the other side runs the
partisans.
Have a bit more patience with newbies. Of course some of them act dumb -- they're often students, for heaven's sake. - Terry Pratchett
A government is a body of people; usually, notably, ungoverned. - Quote from Firefly