Asteroid 349507 (2008 QY) is around 1.2 kilometers in diameter, or around 1,000 capybaras – large enough that an impact event (which won't happen now) could be a worldwide catastrophe.
While the asteroid is traveling too far to pose any risk to the Earth, a possible impact event with it could become a worldwide catastrophe.
That's the point, they're making fun of all the news sources that can't be arsed to give actual measures.
"The forest fire is as big as one million football fields!" means fuck all, but saying "Equivalent to a square 75km by 75km." that's a measure that actually means something.
What's really going to fuck with you is that the fire is mostly confined to the boundaries, so a fire would be better measured by units of length. It's not like you have 75 square kilometers simultaneously on fire, you've got 75 square kilometers burned, as in past tense, and some amount of the outline of that is currently on fire.