It is not clear whether the withdrawer capture in this variant is mandatory or optional. The use of the word 'can' in phrase " All pieces (including king and pawn) can make a capturing move as a Withdrawer" suggests to me that it is optional. I.e., when a Queen in this variant moves from e4 to g4, and there is an enemy Pawn on d4, it can both do it as a Withdrawer move to capture the Pawn, or as a normal FIDE move, leaving the Pawn alone. The Interactive Diagram follows this interpretation.
It is not clear whether the withdrawer capture in this variant is mandatory or optional. The use of the word 'can' in phrase " All pieces (including king and pawn) can make a capturing move as a Withdrawer" suggests to me that it is optional. I.e., when a Queen in this variant moves from e4 to g4, and there is an enemy Pawn on d4, it can both do it as a Withdrawer move to capture the Pawn, or as a normal FIDE move, leaving the Pawn alone. The Interactive Diagram follows this interpretation.