It's technically just a random rock plucked from the asteroid belt. It's just not big enough to crush itself into a neat ball with gravity, like with planets or our Moon
That means someone at NASA made an effort to search for eclipse events on Mars visible by Perseverance and put the right wheels inside the organisation in motion so that they made the rover make a photo of the sun (and deimos). Nice.
But it's also possible some astroenthusiast did the math and emailed it to NASA, and whoever got that endo thought it would be cool and passed it to someone who could schedule the instrument. If you think about your geekiest friend and how they’d react if you sent them something truly unique about their geekdom that they could act on - well, that’s pretty much how every engr/scientist at NASA would react.
Well why would they not remove dead pixels after they download photos? If it is always the same pixel why aren't they simply processed out and replaced with avg of neighbors? If it is radiation noise then they would need a few photos.