“The police story was that they wanted the restaurant to refuse the bikers service, not to hire additional security.”
Waitress have testified that police had visited Twin Peaks warning them about the feud and the high probability of the Cossacks pulling a stunt like this at this meeting.
Again, the reports I saw (possibly since retracted or clarified) said that the officers wanted them to cancel hosting the event, not hire additional security.
And while staff may have been concerned for their own safety, during a “rush hour” event (heavy crowd expected) it was probably not easy to cancel one’s hours.