Question about use of Past Perfect Tense

Could you explain the difference between the two sentences in the quote?

Bates threw the grunt into the sky as soon as we’d made vacuum.

One of the surviving grunts grabbed the carcass and jumped ship as soon as we passed beneath the carapace…

— Blindsight, Peter Watts, pub Tom Doherty Associates 2006

As far as I understand, in the first sentence the author uses Past perfect to emphasize that the one event had happened before the another ("…threw the grunt into the sky as soon as we’d made vacuum" — they made vacuum before they threw the grunt).

However, in the second marked sentence it seems to me that we can see the similar structure and explanation, but still, the author doesn’t use Past Perfect structure ("…the grunt grabbed the carcass and jumped ship as soon as we passed beneath the carapace…").