That's an animation. If you want guards with shotguns, get Armed Guards (unlocked through the Security branch of warden research)
More information needed to solve this problem! The prisoner probably broke rules and got caught. Maybe they beat someone up, got caught with contraband, etc. Possibly they are a higher security grade (e.g. Max, red shirt) and need a cell in a Max-only area. Get a psychologist right away - he will let you see their urgent needs, recent violations, and let you know if their cell is 'too high grade' (if it's not designated for their security grade in 'Deployment'; see the Mega-Guide for more info). He will also let you know if the prison is calm or ready to riot.