I have to say as someone who did video graphics on a Toronto newscast for 10 years my guess is it wasn't someone having fun - it was a typo. We never did stuff like that on purpose and in fact did everything possible to avoid it from happening on air. 

So why wasn't it corrected? The producer probably should have caught it, but I can tell you from all those years spent in the dark of a control room everybody else is too busy to notice the keys.

The director is setting up his/her next shot, the TD is making sure the right camera is chosen and readying the next move, the P.A. is doing time checks to make sure they don't run over and while they're looking at the screen, they're not always paying attention to the graphics.

I was pretty good and didn't make a lot of mistakes because I triple checked everything. But in the odd event I did a typo that wasn't caught, the only one who ever noticed it was me, because it was my only job and I was more sensitive to an error. 

Generally, the only ones who ever really noticed were the viewers - and boy, did they let us know when it was wrong! Glad it wasn't during the social media era or the evidence would still be around!