Gain/Loss on futures contract Reading 40 long, principal, contract, depends

smuggycfa

For LOS 40a where you hedge the principal (naive hedge) the gain/loss on the futures contract depends on the change in the futures price. Maybe I’ve been starring at the books too long, but I thought if you sell a futures contract the payoff depends on what the spot price does, not what the new futures price is at expiration.
Why is it the change in the futures price is in this case?