Don't know why anyone is surprised, the occasions where football fans get together in large numbers without any incidents are the exception rather than the rule. Even if rangers had won there would have been some trouble, albeit to a lesser degree.
God help those travelling to Moscow, the locals will be out in force & there will be no point going to the police. They try to shake you down & if you refuse its a night in the cells, probably safer with the local yobs!
You do see trouble at other sports, but not like soccer
.