I think it is a bit more complicated and subtle than that.
There are lots of variables:
1. It outright says in the article that sometimes it is only free at certain times.
2. You also have to remember that these level 2 chargers can charge from as slow as 1.8 KW an hour to 22 KW an hour. I didn't check the speeds offered for the "free" rates.
3. There is almost always a time limit, at least here in Germany there usually is. It caries from 30 minutes to 4 hours. On the flip side though, if you know you are getting free charging you might just spend more time there and therefore more money.....
Here in Germany the free charging was only if you were actually shopping at the store. They printed a QR code on your receipt and you had to use that to release the cable. Otherwise it cost money.
I get the feeling the UK is 1-2 years behind the EU when it comes to charging infrastructure. Since the beginning of last year places offering free charging are pretty much non-existent.
They were used as, on average, an EV owner was likely wealthier and therefore there was a non-zero chance the person might purchase more.
Whether the stores are baking the cost into the prices of the products is not as straightforward I would think.
Many chargers were installed using some form of government (local or country-wide or in Germany's case EU) support. They might not have cost them hardly anything.
In the summer if they have solar panels (which also may have been supported by some scheme) that might offset the cost as well.
As far as running cost i.e. electricity, yes, there is a chance that that cost might be passed on to the consumer....
Then again, what are all the people who have no cars going to about the millions spent on subsidies for fossil fuel:
https://www.imf.org/en/Topics/climate-ch...0Subsidies ?