Is arborio rice merely refined Brown short grain rice?
Don't know the answer to that and Cook's Illustrated says:
'So the long and short of it? If you're in a pinch and can't find Arborio, look for medium- or short-grain rice for an acceptable—but not perfect—batch of risotto'.
Arborio rice is an Italian short-grain rice grown in the Po Valley. Like all rice, it starts as brown rice before the germ is removed, but you would not automatically end up with arborio just by refining any type of short grain brown rice -- it's a specific variety of rice that has a particularly high starch content and is therefore good for making risotto.