When leaving Walmart, why does an employee stop you to highlight an item on your receipt?

Normally I’ll always stop but today I wanted to try something different. Checked out normal, went to walk out with receipt in my hand and I just kept walking. No beeping from the security things, everything was scanned, but the employee followed me out the store asking me to stop which I was baffled by. He stopped when I got to the crosswalk

So, what’s the purpose for them to stop and highlight? Am I required to stop? Will I be on some list for not stopping? Will the employee get in trouble? It all seems like theater so I wanted to get the whole picture. Thanks for helping