The existence of this megastar was falls under theoretically possible but never discovered.
Analogous would be an albino duck, existence inferred from albinos existing in every animal, but say an albino duck was not observed before.
Discovering bright pink duck would be akin to discovering something that our models cannot account for or explain.
> “But nobody expected to directly detect one like this because we didn’t expect them to be so bright. “Somehow it’s converting magnetic energy to radio waves much more effectively than anything we’ve seen before.”
That's interesting, and apparently unexpected.
The difference is that pinkness in animals is specific to species and we have explanations for why they are pink. And we also have explanations for albinism, but it's not limited to specific species- it's found widely, across the complex life domain.
Find a pink duck? OK, the neighbor painted a duck. Find a population of pink ducks that reproduce and their children are all pink? OK, now we have an interesting situation.
> “But nobody expected to directly detect one like this because we didn’t expect them to be so bright. “Somehow it’s converting magnetic energy to radio waves much more effectively than anything we’ve seen before.”
Why is this magnetar brighter than expected, and how does it convert energy more efficiently?
Astronomers have hundreds of years of experience in seeing things in the sky that couldn't be explained, and either were "entirely new thing we never saw before" (like pulsars) and even theorists suggesting looking for things that only got recognized once we knew what black holes were. This is common. I wouldn't describe it as mysterious, just unexpected.
> We find that the source pulses every 18.18 min, an unusual periodicity that has, to our knowledge, not been observed previously.
The mysterious (as yet unexplained) aspect of it will require updating models's physics to account for its unusual emission properties. The lead researcher herself distinguished it from known types of objects and states "completely unexpected [object]...nobody thought would be able to produce this kind of emission".
Nothing is being downplayed; the history of astronomy is littered with events like this. If they get enough data and can explain it, astronomy will be updated slightly.
The history of astronomy spans thousands of years, a high number of unusual observations will sure to have accumulated over time. But finding an unpredicted aspect of a previously unobserved class of objects is an exciting event carrying a relatively high amount of surprisal. The involved astronomers are clearly excited and being reserved with language is to be expected of formal papers. While not an astronomer, I find the resulting changes in observation patterns exciting to read about and look forward to learning about the unusual radiative properties of such magnetars.
Neutron stars are really surprising, actually, in the sense that their physics look like nothing we have on earth. We will probably be finding unexpected neutron stars and things like slow magnetars for quite some time.
One might even say it's a mystery at the moment.