There’s a difference between being in custody and being followed.
The protester was walking in front of the deputies and was not handcuffed or otherwise restrained.
For some reason you keep trying to make him a victim here so I suspect you might be a Cruz supporter and any excuse to make Trump look bad is fair game.
When a person has been detained and is being moved from a location (being removed for tresspass), the individual is in the custody of law enforcement.
To arrest an individual, law enforcement officers need probable cause. An arrest is characterized by the idea that a reasonable person would not feel free to leave due to the actions of the law enforcement officers. This usually means that the officers take the individual into custody. Custody can mean a number of things. An individual may be taken into custody by driving them back to the police station. However, courts have also held custody to mean any situation in which an individual reasonably believes that they will not be able to leave within a short period of time. A law enforcement officer has probable cause to make an arrest when there are objective circumstances that lead a reasonable officer to believe that there is a high probability or substantial chance that the individual has been involved in, or will be involved in, criminal activity.
It is clear to me that the protester was not free to come, stay or go as he pleased. As such, he was in the custody of the officers and was being escorted out.