I'll take your point on "out of hand". Some kind of trail was required but "brief deliberation" sums up what the trial was worth.
"Spy" is used because "irregular" is something that was not recognised.
at the risk of getting a little off topic, if we read further -
Although it is clear that the status of unlawful belligerents remains a viable and applicable concept in international law, the nature and scope of the procedural rights that must be accorded to unlawful combatants is less clear. Traditionally, at least in theory, unlawful combatants could be killed out of hand, entitled to little more than a blindfold by way of procedure 
Footnote 23 says:23. This rule was specifically altered, in the case of spies, by the 1907 Hague Convention which required that "[a] spy taken in the act shall not be punished without previous trial." Hague Convention (IV) Respecting the Laws and Customs of War on Land, Annex to the Convention, Art. 30, supra note 7..
So spies and other unlawful combatants are clearly viewed differently.