You should first look at support.  If the child is paying over 50% of his own support, he would not be a dependent.

Then you need to look at if this is a "temporary" thing.  My first impression is that the student has permanently moved away from the parents (or vice versa), and they just visit each other.  If that is the case, the child would not be a dependent.

Some things to consider:
Has the student ever lived with the parents in Russia?
Does he go back and visit them in Russia?
You said the parents visit, but do they live with the student when they return?
Is the student's home a place the parent's own, or is it a home the student acquired?