The problem with these stats is that they are based on github data. So only stuff uploaded to gitgub will feature.
This is why there's loads of JS and Python. Because these are hacky scripty languages that everyone writes throwaway stuff in.
What ISN'T in the stats, of course, is stuff that ISN'T open source and uploaded to github. If it included all this stuff as well, then the result would be very different - for one, I would put money on it that C is at the top of the list because there are many millions of lines of C written every day. It's just that most of it isn't and never will be open source. Same goes for C++.