Mr. Gelin, who is black, said he was recording the scene with his phone when Deputy Gallardo, who is white, demanded that he stop. Mr. Gelin continued recording until the deputy arrested him and charged him with resisting without violence.

Deputy Gallardo wrote in a police report that he responded to a call of a victim who was bleeding from his ears and skull. Mr. Gelin, who was recording, approached the deputy from behind and was handcuffed when he refused to leave the area, the report said.

Mr. Gelin said he was in jail for nine hours, and prosecutors dropped the charge after seeing the video from his phone.

“I was profoundly affected by my wrongful arrest,” he said. “It was a traumatizing experience and I think about it a lot. I had a flashback at the meeting and thought it was the right thing to do to call out the officer.”

Mr. Gelin acknowledged that he could have handled the situation better on Wednesday but said that he wanted to make it a learning opportunity.

“Wrongful arrests have lifelong impacts on people and happen more than people would want to believe,” Mr. Gelin said. “I need to be a voice for the people who don’t feel like they have a voice or the courage to express their voice.”

Since the meeting, Mr. Gelin said he had received hundreds of messages. Some have been racist and hateful, but many have been supportive and grateful, particularly from those in minority communities.