Many people don’t understand how card networks work. Generally there are many parties involved in a payment. There is an issuer (usually a bank), acquirer bank, the visa network itself, the payment processor company, etc.

If peering between any of these entities is interrupted, there are sometimes “stand in authorization” that allows the card to continue to work, or people may assume the visa network itself is at fault even if it is not the issue per se.

It’s possible (even likely) that a retailers payment processor is having issues in certain scenarios and the retailer just issues a blanket statement “visa is down” which is actually a misnomer.