I expect that there are tax advantages to holding individual stocks rather than an index fund.
Is finding a subset an active strategy? Depends. Do you do it every day, or do you figure out your subset and then buy and hold for fifteen years?
Is it passive when you rebalance against your target quarterly?
I think we can all agree that it's not passive when you are doing HFT, and anything which involves picking new stocks daily or weekly is active -- but having an algorithm do the rebalancing against your existing target daily and executing when a threshold is met? You're not making new picks, just readjusting against what you've already picked.