So, some context for this. Recently a new feature was rolled out to Tumblr, where you can change or add a community label to a post. More details on it here: https://help.tumblr.com/hc/en-us/articles/5436241401239, but the tldr is posts can be flagged based on some possibly troubling or triggering content for some viewers.

Once the general Tumblr-sphere caught on, people thought this meant "Go nuts, show nuts" was back; as in, NSFW is generally allowed again. However, that was definitely not the case, as nothing in the TOS or other site details was updated to reflect allowing NSFW. This was just an addition that we're (Tumblr users) suspecting is one part of possibly allowing NSFW content again.

Thus the above is why I think photomatt put that post up, perhaps in response to all the inquiries and buzz on the site.

Source: daily tumblr user :)