Technically I believe every communities created with the NSFW tag will auto-apply the NSFW tags on all posts. Maybe the user who posted submitted to a community that isn’t tagged as such (some of them like /c/[email protected]) because the content is not always NSFW.
The only thing we can realistically do is to report these posts. It send a report to your instance admins, who can hide the post from being viewed at the instance you’re at. It will also send a report to the mods of community at lemmynsfw.com in which the post was submitted who can take action on the post itself.