I thought off-duty cops hired for security had the same liability exposure as regular citizens.
Its not just the liability, its the role the Cop uniform plays. Everybody understands what the role of an LEO is and that the LEO is trained and employed to enforce the laws and to detain and arrest people if necessary. Heck, even our local big chain grocery has armed and uniformed security in their parking lots 24/7.
Frankly I'm stunned that a Walmart anywhere would countenance regular employees, even in Loss Prevention, actually fighting with suspected shoplifters out in the parking lot.
I deal with a situation similar to this most every day at work, on duty with a radio outside of school at closing time. Mostly the goals are to prevent fights and egregious drug deals, and especially to watch for non-students of various descriptions intending harm to our students (even if the students in question might deserve it).
Last year we even had a mom and her teenage daughter (not one of ours) walk onto campus looking to kick the crap out of a girl on our campus (the ex-con father had sense enough to wait across the street, the whole thing was obviously the mom's idea). Worse, they even jumped the kid right there in the parking lot right in front of me
I have no idea what the mom expected to happen, but she seemed surprised when she and her 17 yo daughter were restrained and cuffed by our Cops and later handed over to the SAPD on a number of counts.
Just a pair of eyes and ears on a radio out there stops 99% of it, and I wouldn't dream of actually physically intercepting a kid attempting to flee, even where I could. The only time I'll physically intervene is to run interference on a fight, for example in that three-way catfight I restrained wrists so chunks of hair wouldn't actually get torn out, but thanks to the radio help arrived in moments.
I realize this is all pretty pedestrian stuff compared to what the Cops on this site have to deal with, but, the Walmart analogy does apply.
Birdwatcher