Ballroom dancing can be traced back to the 16th century, it was a French Renaissance social dance, ballroom dancing was also a way of separating the upper class from the lower class.
Ballroom dancing is an outgrowth of the folk tradition of couples dancing common in most cultures of Europe. The most famous is the waltz originally from Austria.
I think the people who attacked are cowards. They sneak in and attack people who are minding their own business and enjoying their life without doing any harm to anyone.