If he was able to get into the front, then yes, he should have been handcuffed. Could you imagine if he removed the rifle and started using it? (Don't know where the LE's rifles are kept, but ours were easily accessible if you had any insider information.)
In my day, we cuffed ALL arrestee's. Sometimes going by the book has its merits. If this sort of thing would have happened, we would have a lot of explaining to do as to why we didn't.
Just to play "Devil's Advocate", he was just detaining a man who was acting "strange", so theoretically, he was not being arrested and maybe just placed in the back seat to simmer down?
