Nothing in the Endocannibalism page suggests that any mentioned group ate their own members to the exclusion of eating members of other groups. That topic isn't discussed at all anywhere on the page.
The most prominently mentioned example, though -- New Zealand -- was definitely not exclusive endocannibalism.
The exocannibalism page confirms that the Wari' also practiced exocannibalism.
The article is obviously very basic; I just linked it as a starting place for your research. This is not really the kind of thing where arguments from first principles are productive.
The exocannibalism page that you found does say that the Wari are the only known example of both types of ritual cannibalism, which suggests that it's more of an exception than the rule.
The most prominently mentioned example, though -- New Zealand -- was definitely not exclusive endocannibalism.
The exocannibalism page confirms that the Wari' also practiced exocannibalism.