Your headline is misleading and mischaracterises both the study and what the researchers are saying about their results.
From the abstract of the study:
To search for unbound stars, we then focus on stars with a probability greater than 50% of being unbound from the Milky Way. This cut results in a clean sample of 125 sources with reliable astrometric parameters and radial velocities. Of these, 20 stars have probabilities greater than 80 % of being unbound from the Galaxy. On this latter sub-sample, we perform orbit integration to characterize the stars’ orbital parameter distributions. As expected given the relatively small sample size of bright stars, we find no hypervelocity star candidates, stars that are moving on orbits consistent with coming from the Galactic Centre. Instead, we find 7 hyper-runaway star candidates, coming from the Galactic disk. Surprisingly, the remaining 13 unbound stars cannot be traced back to the Galaxy, including two of the fastest stars (around 700 km s−1 ). If conformed, these may constitute the tip of the iceberg of a large extragalactic population or the extreme velocity tail of stellar streams.
The study looked at 20 stars - seven of them (35%) were heading out of the galaxy, the remaining 13 (65%) were heading inwards.
So, the study found both what it expected to find (stars moving at high velocity away from our galaxy) and not what it expected to find (stars moving at high velocity towards our galaxy).
Nature throws up surprising results. This is not surprising. What is surprising is that the scientists were surprised, as this information about inbound high velocity stars was well published about 19 months ago,
at the University of Cambridge.