Why is the number of referring domains on my dashboard different from the Site Explorer Overview?

If you've added your website to Ahrefs' Dashboard, you'll be able to see the number of referring domains you have:

However, when you click through to Site Explorer, you'll see that the number of referring domains is different:

Why?

Please note that these numbers shown on Dashboard are not real-time, and they are only updated twice a day. 

The numbers on Site Explorer > Overview are the latest values, which you can also see if you visit the Referring Domains report: