There is no such thing as a victimless theft. If there were, this would not be an example of such a theft.
First of all, local convenience stores are not huge companies that can easily withstand losses. They are typically owned by the person operating them. They may be franchises of a bigger chain, but they are owned and operated by local people. This means that they are not equipped to simply “eat” the losses from theft.
The other thing to consider is that even theft from larger companies is not victimless. Leaving aside the ethics of the action, there are still consequences for other people. When a person steals from any business, that business must absorb the loss. What then happens is that the business must in some way make up for that loss. It might, for example, raise the prices that it charges everyone to make up for the losses. In this case, the man’s theft ends up harming every customer of the store. If there is enough theft, the store might have to lay off a worker or reduce their hours because they are not getting enough money. In this case, the man’s theft has harmed the worker.
There is no such thing as victimless theft.