I understand your point. It would have been good to have 11.3 as a separate Module.
However, I reckon that they placed 11.3 Types of OS under "Managing Support" so that the students would know the various OS that they may need to support, along with the (11.3.6) OS compatibility issues, (11.3.7) Vendor life-cycle limitations) and how it ties up in (11.3.8) managing a support ticket
Meanwhile, did you notice that there's no 11.4? From 11.3, it jumped to 11.5 Additional resources.

The only item that has 11.4 tag is challenge live lab: resolve help desk tickets.