alt Hacker News“Correct” here presumably means “some other people are also experiencing problems.” For companies like large banks, with tens of millions of customers, that’s not necessarily very meaningful except for the people who happen to be experiencing the issue.
That's why downdetector shows a chart, which is basically a chart of how many people clicked "I'm having a problem with this service". Of course you get a small amount of people having issues, but if you suddenly see a big spike on the graph, it's a good sign that it's broken for many more people than usual.