Could these white fluffy spots on the wood in the attic be be mold

First, I'd redirect the bathroom vent out of the home. Best place is on the gable side of the house, but straight out the roof would also work. Depending on how much condensation you're seeing, and where it travels after condensing, this could be the cause.

Then I'd do some detective work. Start removing the insulation on the other side of the mold. Look for signs of water damage and follow them back to their source. There could be lots of causes, including a leak in the roof, plumbing problem, a clogged hvac drain line, or condensation on uninsulated hvac ducts. Water can travel a long distance before it finally settles on a low spot, so search far and wide.

It depends.

It depends on the type of mold. It depends on the severity of the infestation. It depends on how many treatments they applied.

Bleach is not sufficient or approved for mold remediation. You may need to use something like MoldStat and even then you may need to take additional steps. If the infestation was bad enough you probably could replace the affected drywall section (and, while doing so, treat the lumber behind it).

It sounds like you live in a communal building like a condo or apartment. If a leak from your neighbor caused a mold problem in your unit then your association likely has a legal obligation to hire licensed mold remediation specialists. I would raise it concern immediately with your management company. Suggest that if action is not taken that you will contact the ombudsman.

You are not responsible for damages caused by your neighbor's leaks. Your neighbor has insurance and/or the association has insurance. If you are concerned, have a professional mold agency deal with the problem.