The commentary explains that where the buyer’s remedy is rescission by option, destruction of the goods or an intervening act that prevents their return may, under the apparent transmitted rule, leave the full agreed price payable.
The reason is that this option is not the same as compensation for a missing component of the goods under defect remedies; here the remedy was affirming or reversing the sale.
Its application depends on the state of the goods, intervening acts and the precise juristic opinion, not a universal rule detached from its conditions.