The man had nothing in his possession.  He WAS considering purchasing a chainsaw with accessories but decided to get another model - he RETURNED the first chainsaw to customer service.

He continued shopping when he was accosted by the store manager.

First, the store manager had the right to INFORM the man that under the Trespass to Property Act that he is requiring him to leave the premises.  He FURTHER has the right to ARREST (citizen's arrest), should the man refuse to leave the premises, but NOT to detain him nor touch or threaten him.

*Arresting and detaining are NOT the same thing.  The Police are responsible for detaining.

Charges should absolutely be laid against the store manager.  He committed a criminal offence by assaulting the man, and likely several misdemeanors for harassment.  In addition, the accosted man should sue in civil court.