Yeah., Dropping a warhead from space and depending on gravity to hit the correct target would require really complex math and with A.I. it’s now possible.
I doubt very much any system could detect, correctly, falling metal with no heat signatures from propulsion.
deorbiting needs propulsion, and quite a lot of energy. Also re-entry generates lots of heat, more so than powered flight. And the thing stays hot.
Rocks don’t just “fall” at orbital speeds.
There are a heck of a lot of smart guys who have been working these problems for decades.