Of course, Smith was photographed in front of the Tennant exterior too, but that was before his exterior was actually decided/designed. The decision to dig out a design not used since 2013 (for Day of the Doctor) for this teaser seems... well, it seems strangely specific, especially when this teaser would've been filmed when the current TARDIS props (of which there are more than one) were out and about, ready, being used for filming anyway. Hmm!
There are like seven different current TARDIS props, though - and they couldn't get one? It's just interesting as the tradition has always been for the first photo to be in front of the /current/ TARDIS -- see the Smith one above - so for them to use one not current is, well, striking.