Cops arrest people without any evidence all the time, then the taxpayers cough up the settlement for false arrest.<quoted text>
But it would be extremely rare to arrest with this minimum of evidence, when this has been the ONLY claim of abuse. The alleged "victim" would need to file a formal complaint
Arresting people for open carry of firearms in states where open carry is permitted is common and almost always results in a payoff.
Unfortunately, cop training does not include any understanding of the law or civil rights.