I think this argument is mostly about whether purpose is there - not about where it comes from.
Designoid entities as a result of anthropic selection effects seem quite possible in theory - and it would be equally appropriate to describe them as being purposeful [standard teleology terminology disclaimers apply, of course].
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").
Sweet, there's another Bloggingheads episode with Eliezer.
Bloggingheads: Robert Wright and Eliezer Yudkowsky: Science Saturday: Purposes and Futures