The Red Cross has a nice overvew of "hors de combat" means:
A person hors de combat is a person who is no longer participating in hostilities, by choice or circumstance. Under customary international law, a person can be placed hors de combat in three situations arising in both international and non-international armed conflicts:
(i) Anyone who is in the power of an adverse party. It is uncontested that a person who is in the power of an adverse party is hors de combat. This rule is set forth in Additional Protocol I and is implicit in common Article 3 of the Geneva Conventions and in Additional Protocol II.[20] It has been confirmed in numerous military manuals.[21] Respect for and protection of persons who are in the power of an adverse party is a cornerstone of international humanitarian law as reflected in several provisions of the Geneva Conventions and Additional Protocols. Practice, therefore, focuses rather on the treatment to be given to such persons (see in particular Chapters 32 and 37).
(ii) Anyone who is defenceless because of unconsciousness, shipwreck, wounds or sickness. This category is based on the Hague Regulations, common Article 3 of the Geneva Conventions and Additional Protocol I, which prohibit attacks on defenceless persons.[22] It is found in numerous military manuals.[23] It is contained in the legislation of many States.[24] It is also supported by case-law, official statements and other practice, such as instructions to armed forces.[25] In addition, respect for and protection of the wounded, sick and shipwrecked is a cornerstone of international humanitarian law applicable in both international and non-international armed conflicts as reflected in several provisions of the Geneva Conventions and their Additional Protocols. Practice, therefore, focuses rather on the treatment to be given to such persons (see Chapter 34).
(iii) Anyone who clearly indicates an intention to surrender. This category is based on the Hague Regulations, common Article 3 of the Geneva Conventions and Additional Protocol I.[26] It is contained in numerous military manuals.[27] It is included in the national legislation of many States.[28] It is also supported by official statements and other practice, such as instructions to armed forces.[29] The general tenet that emerges from this practice is that a clear indication of unconditional surrender renders a person hors de combat. In land warfare, a clear intention to surrender is generally shown by laying down one’s weapons and raising one’s hands. Other examples, such as emerging from one’s position displaying a white flag, are mentioned in many military manuals.[30] There are specific examples of ways of showing an intent to surrender in air and naval warfare.[31]
Which one of those would apply to the four soldiers that were targeted?