I was surprised to see this in the news. I have a local community Facebook group and these outages have been communicated several times on the group before. Actually it's normally it's Tesco that seems to have an issue with the payment system going down across a store, but I'm sure Sainsbury has had the issue as well. I assumed therefore that it was only our store that was affected, but it seems like it was a global/countrywide issue. Would also be interested in seeing more details.
I was wondering the same, especially after the email sent from the CEO last night. It was just an apology and said they're back to normal, with no attempt to explain or give any details. It didn't even mention that they're investigating it, nor that they plan to give more details in future.