That's just bad history and bad... knowledge. Encyclopedias are large collections of reference information. If they change, they change because our understanding of various subjects have changed over time.

Talking about history specifically, it is a pretty poor attitude to have. Our understanding of history has changed a lot, both in accuracy and in how we examine and study history itself. I guess that particular person isn't a big fan of that instability.

Do you know what the scriptwriter or the director intended? This might be a genuine statement of what they believe, but they might be satirizing the knee-jerk assumption by many on the right that everything in the media today is biased towards the left: reducing it to the absurd by having a character say it even about encyclopedias.

But encyclopedias have not been without their biases. The old World Book ones I had as a child had quite a lot more anti-Communist pro-American rhetoric, compared to actual analysis of what Marxism actually was. And historians writing for them can have changing opinions, just like any historians: you can read articles on General Douglas Haig , in the various editions of the Encyclopedia Britannica after WWI , and find him first lauded, then heavily criticized, and then rehabilitated.