The graph is missing the complete hierarchy of the Wirth languages. A very important part of programming language history. They influenced many languages and of course are a direct predecessor to Go. While Go has mostly a C-style syntax, in my opinion, it is otherwise closely based on Oberon.
Also missing is Ada from that same lineage, the entire category of concatenative languages (with Forth the best known example), COBOL, SNOBOL/Icon, BASIC, APL, PHP, Racket, etc. It's laughably incomplete, not a history at all, and "opinionated" is a severe understatement. Was not at all surprised to see that the author's still a student specializing in Coq and similar things. Experience building actual complex system…
The exception is COBOL, which is still important in the way FORTRAN and Java are, but similarly will not affect future languages.