Well, I can't speak for the HA specifically, but in general, bikers are used to getting hassled by the cops for one reason and another and are most often surprisingly cooperative, just because it is easier to go along to get along and let the cops begone. Now get a large group together, get some beers in them and have some government employee act disrespectful and compromising of their authority in their perceived territory and you can get a negative reaction.
Also, I'll have to point out that the article said the bar was "frequented" by some HA and did not implicate them specifically. It's easy to hang that sort of thing on a 1% club because of public image, but such is not necessarily the truth. I think the author was getting at there being a "tougher" crowd in the evening.