First, many repositories are not a single language. For example, this PHP framework is reported as a CSS project [0]. While it has more lines of CSS than PHP, it only has a single CSS file [1].
Second, GitHub has a problem with correctly identifying programming languages. For example, PrimeCoin [1] is identified as one of the most popular TypeScript repositories, but it has 0 lines of TypeScript code. Instead, it has... large localization files with the extension *.ts [2]. BitCoin used to have the same problem, but it looks like GitHub hack fixed it for that particular repository as less popular forks of BitCoin still have this issue.
It took me a few minutes to find these examples, just by examining trending repositories [4]. I'm sure there are many more. So do not be rash in drawing conclusions from this data! :)
[0] https://github.com/laravel/laravel
[1] https://github.com/laravel/laravel/blob/master/public/css/ap...
[2] https://github.com/primecoin/primecoin
[3] https://github.com/primecoin/primecoin/tree/master/src/qt/lo...