The simple version is Labor Party supporters were more inclined to be straight-ticket voters, while those inclined toward the Liberal Party spread more of their votes among other parties.
That’s how the Labor and Liberal parties went from five seats each on the Longyearbyen Community Council, when there was a nine-vote difference immediately after the election, to Liberals losing a seat a day later in the official count, even though they narrowed the vote margin to a mere five ballots.
Beyond that, trying to explain the formula used to allocate seats or ponder “what-if” scenarios if a person (or three) had voted differently is easy to explain only (and then only maybe) if you’ve got a PhD in mathematics (and then only maybe). Or if you actually are familiar with something called the Webster/Sainte-Laguë method.