No Snickers bar was recovered ... this is a big problem for the guard.
A guard is not the adjudicator or decider if the guy stole $1 worth of product or not (a judge/jury is). He can arrest, but likely must use reasonable force to do so. Its not his property, its not his store.
If they guy stole the candy bar from him as a natural person (bar was his) then the analysis would be different.
But here, not his property, not on his property, just shooting some guy who he thinks stole a whopping dollar worth of merchandise? And no candy bar recovered? He's gonna have issues.
A further analysis of that state's citizen's arrest laws would be needed for a more detailed analysis. Maybe he's OK, maybe not...at least legally. Maybe more of a civil matter than criminal.
In reality, the guy who got shot gains nothing from a criminal conviction of this guy; I would not press charges but pursue an avenue that would give me something ($$$).