Because the 3D Document's Reflected Ceiling Plan really looks upward and generates what it sees.
The Reflected Ceiling Plan folder you see in the View Map is just a name, but it uses mostly the same settings as normal Floor Plans with a few changes in Model View Options that suit Reflected Ceiling Plans better.
Compare the View Settings of a Floor Plan View and a Reflected Ceiling Plan View and you will see there is not much difference.
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