As I type I'm wearing a "got freedom?" shirt. Hm.
Anyway, I believe as the video went on the arrested men pushed the limits and were indeed trying to instigate something. Just because you have the right to dance, or to kiss or whatever in a place like a solemn memorial doesn't mean you necessarily should.
At first, they were not disturbing anybody, and I believe the cops should not have approached them in the first place. However, the fact that the offenders pushed their luck until they were forcefully subdued puts some blame on their part. It's really not that hard to just stop, because you don't HAVE to be dancing in a place like that.
I thought it was funny how when the offenders asked "What law is that? That says we can't dance?" and the cop couldn't answer him. That was most likely because in some cases dancing would be considered public demonstration (like in the case of a flash mob) but in this case it was one person, dancing quietly with earbuds in. No "demonstration" there.