I've worked as a retail loss prevention detective for two well-known chain stores. LP staff at big-name retailers such as Macy's, L&T, etc. adhere to a protocol to ensure a productive detainment. In order to make an apprehension, the following needs to happen:
1) The detective must see the person approach the merchandise. (Usually, a suspect will attract attention to him or her self by giving off "alert signals" that LP staff are trained to recognize.)
2) The detective must see the person select merchandise.
3) The detective must witness an overt act that shows intent to commit a larceny. This is usually something like popping off an EAS tag (the thing that makes the door alarm go off), concealing the merchandise, etc. New York statutes criminalize concealment, meaning that if someone were to say, take a shirt off a store rack and put it in their purse, that's enough to constitute petty larceny. However, in practice most DAs will not prosecute and most police I know won't even effect an arrest based on concealment alone. More on this in No. 5.
4) The detective must perform constant, uninterrupted surveillance. This is to ensure that the suspect does not ditch the merchandise.
5) The suspect, with the pilfered merchandise, must walk past all points of sale. It's best to wait until the suspect actually exits the store, as many places these days have merchandise in the vestibules and past the registers. Police prefer that apprehensions be done outside the store as well because it makes the case stronger.
If the criteria above -- which are pretty industry standard -- are followed, then there should never be any doubt as to whether or not a theft occurred. If a detective makes an apprehension only to discover that the suspect did not, in fact, have any stolen merchandise, this is deemed a non-productive detainment and can be grounds for termination and civil lawsuit from the apprehended party.
There's really no excuse for store personnel to ever apprehend someone when less than 100% certain that a theft has occurred. This leads me to conclude that either A) The person in the photo being circulated is NOT MCW (I don't think it looks like him) or B) There was NO misunderstanding. MCW was caught shoplifting, or assisting another in the act, and was not arrested based on the value of the property and his level of cooperation.