I agree its disputed, but i don't think it follows from that that it is both. Like hypothetically (i say hypothetically since this is not the situation at hand afaik) if there was one crime that only applied to non international armed conflicts and one that applied to international, i don't think it would be just to charge with both just because its a bit unclear which is the correct one.
War crimes require a nexus to an armed conflict, and for some war crimes this conflict
must be international.5 For this reason, it is necessary to assess the situation in Gaza
and in Israel to determine whether an armed conflict exists and if so, its nature.
13. The Panel agrees with the Prosecutor’s conclusion that the conflicts in Israel and Gaza
comprise an international armed conflict and a non-international armed conflict running
in parallel. Hamas is a highly organized non-State armed group, and the hostilities
between Hamas and Israel have been sufficiently intense to reach the threshold of a
non-international armed conflict. The Panel’s assessment is that the non-international
armed conflict between Israel and Hamas began, at the latest, on 7 October 2023, when
Hamas and other Palestinian armed groups launched Operation al-Aqsa Flood against
Israel and Israel launched its Operation Iron Swords in response. The Panel has also
concluded that there is an international armed conflict between Israel and Palestine on
the basis either that:
a) Palestine is a State in accordance with criteria set out in international law, for which
there is a sufficiently strong argument for the purpose of an application to the Court
for an arrest warrant, and an international armed conflict arises if a State uses force
against a non-state actor on the territory of another State without the latter’s consent;
or
b) Palestine and Israel are both High Contracting Parties to the 1949 Geneva
Conventions, and that pursuant to the text of Common Article 2 of the Conventions,
an armed conflict between two High Contracting Parties is international in
character; or
c) There is a belligerent occupation by Israel of at least some Palestinian territory.
14. The Panel’s assessment is that the international armed conflict began at the latest on 7
October 2023, when Israel first started responding to the Hamas attack on its territory
by using force on the territory of Palestine without the latter’s consent.
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I also found in the legal report the following that partially explains the reasoning https://www.icc-cpi.int/sites/default/files/2024-05/240520-p... :
War crimes require a nexus to an armed conflict, and for some war crimes this conflict must be international.5 For this reason, it is necessary to assess the situation in Gaza and in Israel to determine whether an armed conflict exists and if so, its nature. 13. The Panel agrees with the Prosecutor’s conclusion that the conflicts in Israel and Gaza comprise an international armed conflict and a non-international armed conflict running in parallel. Hamas is a highly organized non-State armed group, and the hostilities between Hamas and Israel have been sufficiently intense to reach the threshold of a non-international armed conflict. The Panel’s assessment is that the non-international armed conflict between Israel and Hamas began, at the latest, on 7 October 2023, when Hamas and other Palestinian armed groups launched Operation al-Aqsa Flood against Israel and Israel launched its Operation Iron Swords in response. The Panel has also concluded that there is an international armed conflict between Israel and Palestine on the basis either that: a) Palestine is a State in accordance with criteria set out in international law, for which there is a sufficiently strong argument for the purpose of an application to the Court for an arrest warrant, and an international armed conflict arises if a State uses force against a non-state actor on the territory of another State without the latter’s consent; or b) Palestine and Israel are both High Contracting Parties to the 1949 Geneva Conventions, and that pursuant to the text of Common Article 2 of the Conventions, an armed conflict between two High Contracting Parties is international in character; or c) There is a belligerent occupation by Israel of at least some Palestinian territory. 14. The Panel’s assessment is that the international armed conflict began at the latest on 7 October 2023, when Israel first started responding to the Hamas attack on its territory by using force on the territory of Palestine without the latter’s consent.