Reading back through the various definitions, I'm not completely sold on Michael's argument, but at the same time there's really nothing else it can be. There are only two processes in the initiating group, and a grand total of two outputs between them: the project charter and the stakeholder register. Both have their own arrows on the diagram, so that doesn't help us. But the project charter does include the summary milestones for the project, so that could be interpreted (I guess?) as a starting point for the resource calendars as it would set the timeframe we're looking at.
Beyond that, I don't know how much that (or any) answer holds up; I suppose you could make the argument that yes, you may have defined some assumptions regarding availability of certain resources, but considering how the PMBOK guide lays out the ITTOs throughout the book I think this is a stretch, as you would expect that to be called out more explicitly.
Short version: I'm not a fan of this particular diagram, in all honesty. I think it's useful to look at early on in the process to give you an idea of how things are inter-related, but once I got into the weeds I found this to be more confusing than helpful. For the sake of understanding how things work in the real world, Michael's response is probably correct, as in practice you are going to have some of these answers up front "earlier" than the process says you will. But for the PMP exam, I found the questions to be much more straightforward and in line with how the book explicitly defines the ITTOs.
