It is not uncommon for carrier staff to garble legal issues. It is true that the decision is due to "Singapore rules" but it is also true that there is a solution to "Singapore rules," simply one which they have chosen as a corporate policy not to implement.

Not uncommon when there are oddball tax rules for various carriers to limit what they cater on the ground.

Maybe if you ask nicely, they will siphon some out of the F bottle after the F pax are taken care of.