That is a good point, and the intent is/was good. However, it still sadly constitutes theft due leaving without payment. Now, leave and IOU might be different. It really depends on what kind of agreement you have with the establishment. If it was so tight you could leave and come back and pay in full later, likely you would know the owner and/or managers and call them or the police and have this whole thing settled in a matter of minutes (maybe 10-15). If you were that close to them, sticking around to pay in full would not be an issue, and strengthen the bond you have with your local grocer.
My take on all of this is the people that took and didn't pay were thieves, knowingly taking without paying and thinking they would not get caught. Whether or not is an inconvenience that the registered were locked up or not is certainly not at all justification for what is right or wrong. If someone thinks stealing food from a store is justifiable at any level, for any reason, then we are moving to a third world model of rioting/looting thinking before the catastrophe even hits.
Image what it will be like when folks are actually in need of food/services and the options are not even available (gasp, third world as usual).