There is no reason to doubt the translator just because you don't like the study's result.
For a fair comparison, the translator would have to fully appreciate the relevant connotation of every significant word like "different" in every question, and successfully convey the same in Russian. You couldn't just go to a regular translation service and get a good result.
Although I have no faith in a multiple choice test as a predictor of CS knowledge anyway. That is just a horrible test format anyway.