Who created the Klingon course?
Was it made by fan volunteers in the Incubator? Duolingo staff? Owners of the Star Trek franchise? Asking purely out of curiosity.
He's being modest. The specific fans are members of what Marc Okrand has called the qolqoS, the essential core, of the Klingon-speaking community. I just watched him get a medal from the Klingon Language Institute for his leadership of this project. When the owners of the Star Trek franchise want authentic tlhIngan Hol, or Marc Okrand wants proofreading, they reach out to this group.
You need have no concerns about getting the true language, or the best information on the language. As in any language, there are some dissenting opinions on the nuances, so I'm pleased that an articulate proponent of one of those opinions is active on the forums, to keep us balanced. Within the limitations of Duolingo, it's like you're learning Klingon at the heart of the KLI.