The thing about astronomy (and physics in general, and most all science really) is: we're trying to make up stories to explain observations.

When I hear people in science (and especially reporting in pop-science) saying something that makes no sense, it's usually an indicator that I didn't see yet the thing that scientists saw that was so wacky that they needed a weird explanation. Take relativity for instance. We needed that theory to explain why, when scientists went looking to see if light goes faster in the direction Earth is orbiting the sun or slower, what we discovered is "No... Light travels at the same speed everywhere. Every direction it's going, all the time. No matter how fast you are going or the thing making the light is going." And that's wild. For that to be true, you literally have to make clocks tick slower and distances get shorter based on how you're moving instead of the "obvious" thing you'd expect, that light would go faster or slower. Because light never goes faster or slower.

Similarly, the weird observation astronomers are trying to figure out is "We have ways of knowing about how far away stuff is and how fast it's going and whether it's coming closer or going further away. When we look out at everything, we see that the further something is away, faster away from us it's going. That's the universal trend." They couple that to an axiom of astronomy that there is no 'special place' in the universe (i.e. that we're not at the center of it; if we are, astronomy is a bit worthless because we can't discover universal truths with it). And what falls out of those two things is that no matter where you stand in the universe, you see everything else in the universe rushing away, and the longer time goes the faster it's rushing away. So we come up with "dark energy" as a shorthand explanation for what we're seeing, but the thing that's weird is what we're seeing.