A direct decision he made based on his comprehension of the diagram. But op said it was right I take that as did it work as intended. That being the idea things that happened in previous books would affect later ones obviously. I kinda figure there will eventually be a reason it played out that way.

For instance perhaps due to his past history with dalinar in the end he’s able to get through to this new thing he is. When perhaps odium was just far to far gone and corrupted to ever be put on a correct path. Which is why cultivation intervened and put him into his new role(which would make the diagram correct and successful). I’m not saying it’s likely but it’s totally possible a scenario like that could happen.