It was hardly like they could expect the Doctor to be familiar with shapeshifters or any sort, let alone ones that transformed into dragons. Thedas had its own unique mythologies after all, ones that this world didn't seem to have equivalents to.
"I tend to have trouble talking in that form, so I don't know if that'd help." It wasn't impossible for him to do, it just took an intense amount of effort at present. It was a shame that the Archdemon's ability to talk in people's heads hadn't been kept when everything was purified. "Especially since I'm probably a pretty tiny dragon..."