The linked article which is not a court ruling, it's a report from the "Office of the Prosecutor", says:
"While Israel maintains that it is no longer occupying Gaza, the prevalent view within the international community is that Israel remains an occupying power under international law, based on the scope and degree of control that it has retained over the territory of Gaza following the 2005 disengagement. In accordance with the reasoning underlying this perspective, the Office has proceeded on the basis that the situation in Gaza can be considered within the framework of an international armed conflict in view of the continuing military occupation by Israel. The analysis conducted and the conclusions reached would generally not be affected and still be applicable, if the Office was of the view, alternatively, that the law applicable in the present context and in light of the Israel-Hamas conflict is the law of non-international armed conflict. Given the crimes of possible relevance to the present situation, which are substantially similar in the context of both international and non-international armed conflicts, it is not necessary at this stage to reach a conclusive view on the classification of the conflict. Additionally, as the protection accorded by the rules on international armed conflicts is broader than those relating to internal conflicts, it seems appropriate, for the limited purpose of a preliminary examination, in cases of doubt, to apply those governing international armed conflicts."
So they're basically just discussing the context for this (whether the situation meets some legal criteria to get to the next stage, by the way it didn't). They say it's not really necessary to reach a conclusive view (i.e. at least the prosecutor has no conclusive view, not to mention the court) because it doesn't affect the outcome of this legal analysis.