Most of the victims are adult men, and when archaeologists find a mass execution of men they usually assume they are looking at war captives. There is not much evidence, though, that the Lambayeque people were warriors. Their sites are undefended, their art does not feature warfare, and weapons are not prominent in their tombs. This has led to some strange speculations about where these victims came from, like this one from Haagen Klaus of the University of Utah:
All the dead in the newfound pit were likely willing participants from local communities engaged in a ritual that celebrated death so that "new life could emerge in the world," Klaus said in an email to National Geographic News.
I think it is more likely that there was some warfare in the Sicán world, however little their culture emphasized it, and that these men were the victims of it. Since the site is in many ways unique (so far) it is very hard to know.