This in a ninja release on twitter, but no official words on bitcointalk (some people mention the twitter link 2 hours later though) . At first, somebody caught the news on twitter, and bought NEM/XEM. However, some holders went to bitcointalk and they didn't see anything in this thread; they thought some people was pumping it, so they dumped it. It created a massive dump FOMO. However, it's morning now in the US, so I think NEM should go up from now. Words about the update are spreading in Slack/telegram/Trollbox/Twitter.
Update the news :
https://twitter.com/NEMofficial/status/790808820163366912