If you have an understanding of how Kentico works in general you'll know that objects can be global and site specific. Anything that has a TemplateSiteID populated in it, means that global template, which was assigned to a site, was updated.
Think of it this way, pretty much everything in the Site Manager is a global object. Some can be assigned to specific sites and some cannot. If you update one of those global objects and it's being used by 1 or 2 or 100 sites, all those sites using it will be updated.
To answer your question
JAA wrote: Im curious how the content staging UI knows how to classify this under Objects->Global Objects section
as I mentioned previously, its hard coded in the XML that defines that tree you are selecting the site or global objects from.