That second X-ray defense only works because the white rook is protected by the white queen from above. If that weren't there, the black queen takes rook.
The point is valid that defense lines do not stop at enemy pieces in the current board configuration. They are "X ray" because they look forward to a future board position where some opponent's piece has moved out of the way (perhaps staying in that line of attack, susceptible to being taken).
> In general, defensive tactics and puzzles are underrepresented in chess literature and resources.
I play a lot of puzzles (Storm) on Lichess, and this hits hard. I can spot good attacks, but not good defences because it’s vastly underrepresented in my training.