My Guess:....The police chief made it crystal clear before Obama’s visit, that he expected them to act
‘professionally’, meaning, don’t straight out embarrass the president, OR ELSE! Their pensions, future evaluations, future assigned duties and locations, their scheduled promotions were clearly on the chopping block.
Yes. The police chief has a department to run. He can’t tolerate insubordination even if HE thinks it is justified. He’ll turn a blind-eye to the grumbling, but any public displays would have to be dealt with.