While what you say about drawing conclusions is maybe true, it does not seem to have started with modern scientists. Rather, my takeaway from the article was that everyone is still playing by Descartes’ rules: that is to conflate intelligence, language, and consciousness. So instead of trying to redefine that basis, researchers are simply going with it (however flawed it may be) and saying, “well, if language and intelligence are the only sure ways to detect consciousness, then here are a whole bunch of animals that exhibit intelligence, language, or both.”