If I had a guess, I would say a micro culture is a culture that presents itself on a small scale, unlike a full city or nation it may be only within a neighborhood. Micro cultures seem to consist of less than 1000 people and their group is closely tied to their specific habits and community. Gated communities are micro cultures, where everyone trims their lawn and hedges the same way, paints their house in the same color palette, keeps a similar theme of lawn decorations, lives the 'cookie cutter' life.
Closed would mean that they are either unwelcoming of new people into the community or very resistant to changes to their culture, usually a combination of the two, since new people might go against the grain and offset their happy lives with new customs. HoA's tend to be closed micro cultures, since they have strict, rarely changing rules for how their community behaves.
When it comes to Halloween, some neighborhoods don't celebrate, and when someone who does celebrate moves in it can create quite a stir. The sudden appearance of ghosts, jack o' lanterns and skeletons can upset neighbors who are against the holiday and lead to becoming an outcast within your own neighborhood. Some make take more extreme actions of calling the police or city citing ordinance violations of some kind, in an effort to stop the 'offender' from setting up a Halloween display. Others simply make their displeasure known in a more passive way, usually leading to the 'offender' being shunned by the neighborhood.
The person who is singled out can either keep celebrating and try to brush off the irritated neighbors, stop celebrating to appease them or simply move away to some place more welcoming.
Halloween can be a very polarizing holiday in some areas. When an entire neighborhood has their porch lights off for Halloween, it can make being the only celebrator on the block pretty depressing. Kids rarely visit the single house in the neighborhood that hands out candy.
It all comes down to an 'insider' v 'outsider' thing, us v. them mentality. When kids that are obviously from outside the neighborhood come around on Halloween, it bothers people who are protective of their lifestyle and stubborn to the very idea of change. If those kids will come around on Halloween, then what's next? People like them could move into the area and 'ruin' our happy way of life. It's not a pleasant way of thinking, but it's how some small communities end up.