I assume 1 is pulling only from github.com public projects. Many companies A: don't make their code public, B: probably use github enterprise/other hosted solutions (esp including not git based)
2: Also skews towards a certain demographic
2: Also skews towards a certain demographic
It's very hard to qualify the effect of those biases though: for example how does the public/private repo ratio differ between languages ? Good luck giving a trustworthy answer to that. Apart from looking at lots of different source kinds, one thing that's fairly trustworthy is the trend of a specific language in a specific source.
On that topic, looking at the "SO questions" metric of the first link, C and C++ both have a strange regular spike in the last quarter of each year. I attribute that to new CS students flocking to SO at the beginning of their term. Another fun trend to look at is the hourly google searches over a week: the weekdays / workhours spike is much more pronounced for some languages than others.