Earlier quoted context omitted.
Imagine a guy and two of his friends comes, calls you a bad name, has his friends hold you and beats you up. You try to resist, and when you have the chance, run away from them. The story published in newspapers about the incident is "wizeman attacks a group of nice young men minding their own business, steals their wallet". "All data" != reality...
That is not "all data"
If you mean "but in the real world will have way more stories from other sources about other things" sure. But doesn't change anything if you have "all stories printed". The distrubution matters. All or most of them can very well be biased and not reflect reality.
And that's for factual matters. Let's not even go into political matters. Like in 1920s South most newspaper stories would be biased in favor of Jim Crow, few would be against it.