They said a few months ago that they were leaving Halloween in the hands of the players this year. They are running all past Halloween maps and bosses and releasing the community made content they like the best, but were not making an event of their own as they were working on a new update.
As of this week, that update is the Alien Invasion, so you are correct, they are not running concurrent events. Halloween maps are on and this year’s new items will not be Halloween/Full Moon restricted.
Traditionally, the Halloween maps have always run well into the first weekend (and beyond in some cases) of November, so it should be perfect timing on our part to catch some last minute costumed shenaniganry.
Just in case I’ve gone nutters and misinterpretted things drastically, the information I used is based off of this post.
Sharp-eyed readers may have noticed that there’s something missing from that list: Halloween. The reality is, if we produce a holiday-specific event map this year, it means we’ll have to stop working on everything else. So: We’ve decided to turn Halloween mostly over to you. This year’s Halloween Update will be a showcase of all the best Halloween-themed community content (items, maps, taunts and unusuals) you guys can come up with. We’ll also be activating every one of our past six Halloween Updates, so there’ll still be plenty of spooky holiday-themed game modes to play.
Over the next month we’ll be looking through the Workshop for anything tagged “Halloween”, so if you’ve been working on an item you think would be perfect, make sure you get it submitted and tagged before October 18th, 2015.
Plus, if you didn’t already have enough incentive to submit to the Workshop, we’re changing our restrictions on Halloween items this year. Normally they’re only visible to players on Halloween and full moons. This year, all newly selected Halloween-themed items will have NO restrictions put on them, and may be viewed year round. (So don’t get too gross or out-there with your submissions.)