They were not disrupting the event. They were being harassed. They committed no crimes. They were arrested for being Christians.
When you go to a demonstration with signs and a bullhorn; you are indeed disruptiong the event. They were harassed, because the ONLY reason they went to the event was to harass event goers.
Again, this has little to do with Christianity; this was a group of people out to show their power and to garner attention; Christianity was the excuse these people used to get attention. I find very little in common with the actions of this group and the teachings of Christ.