I don't think the title "Graph of All Human Languages" is correct. Among the more prominent omissions, it doesn't seem to include creoles and sign languages. Besides, the page doesn't claim to be a graph of "all human languages". This would be an impossible task, since determining what counts as its own language is subjective and often hotly debated.
My mistake! Misunderstood the underlying dataset. Not sure how to edit it though. Thanks for calling it out.