[JRKrause]

The word 'unexpected' doesn't appear in the article. It's a fairly safe bet that the team of people capable of hitting a 581 foot object 6 million miles away with a 13,000 mph slug would have expected the ejection of material from the impact.

[RecycledEle]

Correct.

NASA knew there would be rubble put into orbit around the asteroid.

The idiot author of the article has embarrassed himself, his company, his industry, and his advertisers by thinking orbiting ejecta was "unexpected."

[jeroenvlek]

You're right, I interpreted "unintended" as "unexpected", because I assumed that if you know this before you do this then you know what to expect, so it must also be intended.

[mannykannot]

Certainly, but to the person who wrote the sub-heading (I suspect an editor rather than the article's author), it presents a "previously unanticipated risk." The further you get from the source...