No, you didn't imagine it; he was there in preparation for his appearance in the 50th anniversary show, in November. The show’s costume designer, Howard Burden, described Hurt as a “dark Doctor” and added:
“There was a gap between Paul McGann playing the Doctor [#8] and Christopher Eccleston [#9], when we didn’t see a regeneration, and John Hurt will fit into that gap. He is a past Doctor, not a future Doctor.”
Some fans are speculating that this "dark" Doctor is responsible for the destruction of Gallifrey -- that would be interesting! But whatever Hurt's role, it screws up the numbering of the Doctors (unless they're going to call him Doctor #8.5).