To be more specific, I often find that ethnographic is used interchangeably with ethnological, when they don't mean the same thing.  
 
Also, as is I suspect the case in the the example in question, some people now seem to be using "ethnographic art" as a substitute for the old terms of "tribal art" and "primitive art", both of which have lingered on in some art circles but seem to be fading away finally. ( I have also seen this called "Indigenous Art" as well, see here for one randomly picked example: http://collegerelations.vassar.edu/2006/2176/ )
 
For a hybrid example using the word ethnographic, Bonhams the auction house has "Tribal & Ethnographic Arts Departments" which they describe as:
 
"Bonhams' Tribal Art department in the UK and the Native American, Pre-Columbian & Tribal Art department in the US cover between them ethnographic works from the Americas, Africa, Oceania and Australia. Consisting of sculptures, works of art, utilitarian artifacts and ritual objects ... "
 
Try googling the words ethnographic + art and you will see what I mean.
 
As Tom rightly points out, it is not appropriate to apply the term ethnographic to Pre-Columbian artifacts, nor to unprovenanced artifacts in general, since they were not collected under "controlled" conditions. 
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