I like the apartment complex case study that you mention.
A lot of men try to use direct game in their apartment complexes and cause a mess by pooping in their own backyards. It's generally not advisable to date within your own apartment complex.
In larger apartment communities (I would call that 200+ units), you might be able to justify dating someone in the complex under one of 2 scenarios.
- If you are in a mid-rise or high rise building (4+ stories), the woman lives on a different floor as you do, and you're not likely to ever go to that floor. It's still possible you might run into her in common areas, but some men are comfortable with that risk level, especially if you're only seeing her 1-2 times a month at best.
- If you are in a complex of garden style buildings (multiple 1-3 story buildings), the woman lives a few buildings away and you're not likely to see her walking to/from your car. Like the last scenario, it's still possible to see her in common areas but the risk is mitigated if her building is not close to yours.
In the case of your friend, he's likely meeting women who live in the same complex and then dating their friends who don't live in that complex. That's what's happening at the barbecues, non-commercialized pool parties, and potlucks. That's social circle game, which I consider to be an A Tier form of game.