It is a loophole.
Imagine it like sending a letter.
If you send a letter to iFollow asking to stream the match, they will look at the return address on the letter, see that you're in the UK and sends a letter back telling you no.
What a VPN does is act as a middle man.
You send a letter to a middle man in another country (VPN), who then sends a letter to iFollow pretending it's for him.
iFollow sees the address of the middle man abroad and thinks "oh they're in a different country" so replies yes, allowing you to stream the match.
The middle man then passes that iFollow response along to you, so you end up with a positive response.
Source: am nerd