This doesn't necessarily mean relativity's wrong, what it means is that there are parts of cosmology that we can't explain using relativity and hence have placeholders there whilst we work out what they are.

Of course relativity could be wrong, and a new theory might not need the placeholders, but in that case it's going to need to explain everything relativity does, and the formation of galaxies and the expanding universe, all whilst not having too many arbitrary constants.

For one thing relativity breaks down on the quantum scale, and there's nothing in the math to explain it.

Einstein spent the last years of his life trying to figure out how to merge his theory with quantum mechanics.