It was Agatha all along...

Listening to a compelling theory- it almost has to be…
Like Westview is Wanda’s creation, the Witches’ Road is Billy’s
Most everything in his room is represented on the road and so much early dialogue between he and Agatha (and Rio) points to all of this being his
He wasn't even in the room when they opened the Witches Road, so how did he create it?