FAR more likely that the antenna for the radar was outside the hut.
There may have been one slaved to it, inactive, inside the hut to
demonstrate what's going on upstairs.

There are plenty of good reasons why such a demo wouldn't work as described,
from killing the detector with strong reflections, to massive
re-re-reflections inside the building, to the fact that radar relies on a
"pencil" beam that wouldn't survive through those walls in any rational way,
and so on.