Earlier quoted context omitted.
That's a very strange statement, since Chinese and Japanese are not at all similar languages. There are some loanwords, the shared writing system and a lot of historical and cultural, err, interchange, but they have no shared linguistic ancestor and grammatically are just about as different as languages can be. Linguistically, Japanese and Chinese have about as much in common as English and Navajo.
They are similar because they are both logographic languages. The MIT team should of added logographic languages in their experiment for the same reasons in this blog post: https://blog.fluent-forever.com/logograms/
But a language is not its script.
By approximation all modern languages that have been written have been written in the Latin script. That doesn't make them "similar languages" in any real sense. And conversely, many languages use several different scripts for the same language in different regions/groups depending on politics.