It's the reporting. This wasn't a peer reviewed scientific discovery, and it didn't claim to be. It was just a paper that laid out how the experiment was done, and what the results were, nothing more. Just because IFL Science, like every other tech/science site, picks up the story and hints at trips to Mars in a matter of weeks, doesn't mean that's what the experimenters were claiming.
This is how science works. You do experiments, you post your methods and results. Other scientists may do the same. If there is enough evidence that something may be at work, you do more. If you end up showing that everything we thought we knew about the universe was wrong, THEN YOU START CHANGING THE TEXTBOOKS.
The law of conservation of momentum, like all scientific laws, comes with the caveat that our understanding of how the universe works is correct. They are not immutable. Given reproduceability, predictability, and strong empirical evidence, it probably is correct; but that doesn't mean it may not need "tweaking" in the face of new evidence. It could also be that no scientific principles are being broken here, it's just there's something else at play we don't understand.
People who claim otherwise are really just religious zealots in a lab coat.