FWIW, my local political group had some discussion about this and we actually did some digging. The Seattle people are not actually a formal BLM group or entity; they're part of a local group known as Outside Agitators 206. This Seattle BLM FB page literally went live just yesterday; the two big names involved with the stunt are the ones running both groups' pages, though they're trying to deny a connection to each other.
Go ahead and call Mara Willaford to let her know how you feel!
https://twitter.com/alyssa011968/status/503272265077628928
Wouldn't be surprised if this group is involved with the same group of anarchist radicals who were always the first to escalate to violence during Occupy and the Gaza protests. It's certainly not matching up with the general MO of BLM.