Well, no. What the billboard is doing is making a statement that the disarming of the Indians allowed these atrocities to be committed.
I fail to see how this is derogatory to them. Its historical accuracy is of course another question entirely.
so....It sounds like Elizabeth Warren has more Indian blood than the woman doing the complaining here.
The massacre at Wounded Knee started when the Army sought to forcibly disarm the Native Americans they had rounded up.