and it would be equally appropriate to describe them as being purposeful
Especially if you unpack "purposeful" as meaning "stimulating that portion of the human brain that evolved to predict the behavior of other entities". ;-)
The real confusion about purpose arises when we confuse the REAL definition of purpose (i.e. that one), with the naive inbuilt notion of "purposeful" (i.e. "somebody did it on purpose").
That should not be the definition of purpose - if we are trying to be scientific. Martian scientists should come to the same conclusions.
"Purpose" - in this kind of context - could mean "goal directed" - or it could mean pursuing a goal with a mind that predicts the future. The former definition would label plants and rivers flowing downhill as purposeful - whereas the latter would not.
Sweet, there's another Bloggingheads episode with Eliezer.
Bloggingheads: Robert Wright and Eliezer Yudkowsky: Science Saturday: Purposes and Futures