Interference with Fielder - Batted Ball

[Blue37]

My summer league uses OBR with minor modifications, none of which impact this question. We had our qualifying test Saturday, and this question was asked:

R2, no outs. Ground ball to F6. R2 interferes with F6 as he runs to 3rd. Despite the interference, F6 is able to field the ball and throw the batter-runner out at 1st.

The test was multiple choice with the posibility of several correct answers. The answer key stated R2 stays at third and the batter-runner is out at first.

Is this the correct ruling for OBR? How about for Fed? Would a change in the number of outs impact the ruling? What if there were runners on 1st and 2nd?