Unusual interference play

[Bluefoot]

Unless the runner on 3B intentionally interferes with the F5, then how can he be ruled out for interference? He is entitled to remain on 3B. (as long as he does not interfere with F5).

Do you think that R1 should have vacated 3B so F5 could catch the pop up, and by doing so put himself in jeapordy of being doubled up for the second out on the play?

What I further do not understand is how can you rule R1 out for interference, and not call B2 out on the play? If the attempt to catch the ball is declared interference, then doesn't the "interfered-with out" have to be recorded as well?

When a spectator interferes with a fielder making a catch and spectator interference is called, you don't see the spectator being called out, and a foul ball is called on the batter, do you? No you don't - the batter is called out.