It was for AOB. He had throat surgery to remove nodules on his vocal cords and couldn't speak/sing for a while. The first song he wrote for the record was Tripoli which he had to sing in his head because until he could sing again.
I don't think the singing lessons were an idea of his then girlfriend. I remember him saying he had to re-learn how to sing after that and since his nodules were cause by the way he sang before, he had to learn to sing correctly. He recorded AOB with this new singing method which is why there's no hard screaming on it like on previous records.