Im familiar with who he is. At the time his claim to fame was coming up with Nathan Barley, which is why I suspected there was more than a little jealousy there.
He got more famous and acclaimed since black mirror.
I get the jealously part, but the highbrow part seems off to me. Brooker has always shown much more interest in distinctly lowbrow art forms such as video games. I don't think he is sneering at Banksy because he thinks we should be looking at the paintings of the Old Masters instead.
Right but he knows guardian readers think that and he's pandering to their snobbery with his comments about Banksy rolling around in the pop culture mud.
At the same time it's painfully obvious it riled him up being a more obscure and less famous equivalent of banksy.
(Also, if you're familiar with Charlie Brooker's output, he's not really a 'highbrow' type. He started out in games journalism.)