Oh, you're right! I did read about that, but had forgotten it. Maybe this guy's letter was part of that batch. The article says he got it on the 17th, so the timing seems about right.
Those "error" letters were sent to those in the UK using EU laws and European Court of Justice Rulings and this man was trying to get a British passport using UK immigration laws. UK immigration laws and the EEA Regulations, are nothing to do with each other and are not interchangeable.
According to the press, this story was because he thought he was a British citizen and over a year ago, he applied for a passport with his UK birth certtificate which he said named his British father. His father was not married to his mother at the time of his birth and he was refused a British passport as he wasn't born British via his father and until he registered? (ksand will know) he wouldn't be British.
He applied for an Australian passport, which he got. He had a prior arrangement that he would be allowed back in the UK after his holiday to sort out his British citizenship.
He applied for Right of Abode in the UK and was told he couldn't have that as he wasn't British and was again told that he needed to register? first before he could become British via his father.
It then seems he did nothing about this and a year later got this letter.
He is born British, but via his Australian/British mother and not via his British father. She was born in Australia to a British parent, making her British by Decent. She can't pass on citizenship to her son unless he was born in the UK, which he was. Therefore he is British born via his mother.
UKVI only looked at the claim to citizenship through his father and not through his mother.
Unlike the US, being born in the UK does not make that person a citizen.