Okay, I have two perspectives on this Wally world thing....
I tend to do most article shopping at Best Buy. I have never, not once, been physically stopped and or detained by security. Many times the cashier asks that I please take my bag to the security desk at the doors and let them sign my receipt. I have no problem with that. I have been ASKED to show my bag, never ordered, never forced. I have once or twice refused, just to see what would happen. The person looked at the bag, then looked at my receipt, signed it, and let me on my way. Never once has undue physical contact been employed. What was done to sousana has NO excuse. Maybe, maybe had their been a specific and clearly specified reason (ie - we have you on camera and believe you have shoplifted) for the stop, presented as a verbal and polite request providing the reason for the stop and a request to check the bag, all of which being ignored by sousana.....but that didn't happen.
Secondly, I was an employee of Best Buy for two years. One thing that was constantly reinforced, in part due to the occasional belligerant customers, was that you never, EVER, EVER involve yourself in any kind of unwanted physical contact with a customer. Period. The only time I'd ever seen that rule broken was when a kid tried to run out of the store after having been confronted for shoplifting and requested that he empty his pockets. There was videotape of the incident, and the LP rep detained him in the store for the police. I see the situation that either 1) Wally World is to blame for advising it's employee incorrectly, or 2) The employee is to blame for overstepping his bounds.
Did sousana overreact? I can't say, I wasn't there, don't know exactly how it went down. If the employee just used a light touch and asked, then yes. If the employee physically and forcefully grabbed and pulled....no. Also of note....as I understand it sousana was carrying at the time. I don't think it would have been at all prudent to escalate an altercation like this, in such a public venue, while carrying. An overzealous legal-beagle could make that a problem. Considering all the options available (I don't consider being meek an humble and allowing an employee to manhandle me an option), not that my opinion is of any great weight, contacting the police was a proper choice.
BTW - I didn't notice this...might have missed it. Did you request that the employee remove their hand and let you go?