After further investigations, it seems the horizontal stud only goes in 20cm into the wall to the right and is nailed there to a vertical stud. It doesn't feel like it can bear much load since the white shelf and the newer flat horizontal 2" 4" should look like bananas.
Or?
Forget the question about the heart wall. Wikipedia explains it pretty well
I don't think it's a heart wall though since it doesn't run in the lengthwise direction of the house. However, the next wall where I'm going to move a door does, but that will be a later problem. And a glue-laminated beam should probably solve that problem.