To begin with, there is the problem of International Private Law: Which system of laws applies to this alleged tort? The law used to decide that is the Dutch PIL statute for torts, the WCOD. (Lest this become an everlasting regression, the rule is that you use the Private International Law statute of the forum.) However, the WCOD has only been in force since 2001, and does not as such work retroactively. Hence the first cheat: the court decides - correctly - that the statute more or less codified pre-existing law, and then concludes that that is enough to make it applicable to a tort committed in 1947. That last step seems a little dodgy to me. I'm willing to accept that the rules codified in the statue already existed in the 1990s, or even 80s, but in the 1940s? Can we see some case law for that?
Then we get to the big problem: art. 3(1) WCOD declares that the lex loci delicti rule applies. The law of the state where the tort was committed is applied to the case. However, in this case, the alleged tort was committed in the Dutch East-Indies, a state that was at the time distinct from the Netherlands (Kingdom in Europe), and which hasn't existed since December 29, 1949. Now it need not be a major problem to apply the law of a state that no longer exists, but the court thinks that applying the law of a country that hasn't existed for more than 60 years would be pushing it. Which brings us to the next question:
If not the law of the Dutch East-Indies, which law should it be? Logically, it would have to be the Netherlands (Kingdom in Europe) or Indonesia. Since the perpetrators of this crime were Dutch military personnel carrying out orders of the Dutch colonial government in what was, at the time, part of the Kingdom of the Netherlands, the court argues that the case is more closely connected to the Netherlands than to Indonesia.
This seems, to put it mildly, a curious conclusion. One might just as easily argue that the case is more closely connected to Indonesia, the successor state to the Dutch East Indies, the state of the victims, and the state that claims to have existed since 1945, or barring that since the 1946-7 Linggadjati Agreement.
Paradoxically, it is the Indonesian plaintiffs who benefit from this conclusion. After all, we might assume that Indonesia does not have the kind of stringent war crimes legislation that the Netherlands has. Although presumably they have a civil law wrongful death tort, under Indonesian law there would probably be more scope for a "following orders" or "military necessity" defence.