Definitely a typo on the streamers part, they claim it has 2048, which is the same exact spec as the hd 7970. Probably got the two confused.. 7970, 7790...
as for the memory interface, it's possible that it has double the bus width as the reference, but i'm not 100 on that.
Yeah that makes sense about the typo. Although I'm 99.99% sure that the 7790 is offered strictly in 128bit which was one of its downfalls. But man I'd be so pissed if I bought Diamond's card based strictly off of their specs. >.<