So maybe this is a case where we have to ignore the "right" answer as implausible and stick to our old "wrong" assumption because it actually makes more sense.
And, honestly, that's a "wrong" assumption that most of us have been making for nearly fifty years or so. I rewatched "The Apple" before writing those chapters, but it never occurred to me to scrutinize any screencaps in detail. Just watching the ep on TV, as originally intended, it sure seems as though the Vaalians are simply bringing baskets of fruit.
Certainly there are no close-ups or dialogue establishing that the explosive rocks are being used as fuel.