Personally, the writer is slanted towards law enforcement here. Otherwise they wouldn't bring up who was who and who they were affiliated with.

But the bottom line that everyone can agree on is that the Cossacks crashed the party. Yea they might have been set up by the Bandido's, but that is almost impossible to know. Of course they will tell everyone they were invited, otherwise they will look dumb. And if it was a meeting, more than 16 Bandido's would have showed up.