I was about to post the same thing.

This meteorite impacted Mars a zillion years ago. It was later cover with regolith due to dust storms, etc. The covering regolith later eroded away to expose the meteorite.

Jacob Samorodin made an additional comment that is interesting:

"But if it fell to Mars hundreds of millions or billions of years ago,
when there was still a thick martian atmosphere, why haven't acids
and oxygen from the "wet" Meridiani epoch eaten it away by now?"

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The regolith of Meridiani was probabably moist with dilute sulfuric acid a couple billion years ago. For hundreds of millions of years, the plains of Meridiani have been bone dry. If that meteorite had landed when the soil was still moist with sulfuric acid, it would now be a nice example of iron pyite. This highlights the basic problem with Mars: Everything we see on Mars is incredibly ancient (billions or hundreds of millions of years old). Our intuition is based upon on a world (the Earth) where most surface geology is only thousands of years old. Our intuition is helpful when we're studying Io or Titan but it deceives us when we're studying Mars.

Gary