Default distro varies for different repos

I have two different repos with the same .travis.yml (dist is not available there), but one of them is public on GitHub and the other is private. What I don’t understand is that why the newer public repo has the default dist set to Xenial while the older private repo has the default dist set to Precise.

Build for the private repo (Build dist: precise):

I came across this blog article:

Is this related to my issue above?
Please explain.

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