@themarkymark messaged me that this move may have been triggered by a Korean exchange that recently added STEEM and SBD to their trading roster, although those who started trading it over there didn't quite seem to understand (or should I say, still don't fully understand) the difference between the two assets. I also found this post by @dksart on the subject as well:

Link: Korean Exchange UpBit.com Causes A Price Spike In SBD Making SBD Twice The Value Of STEEM