You popped off all the old tile without damaging the ditra mat?
My first question would be how did that happen? Was the tile not bonded well? Did the previous tile become loose and broken before you removed it?
A good tile job should not have separated from the ditra so easily. I would hate to say it's ok to tile over what you have if there was issues with the subfloor (deflection) or they used mortar that wasn't mixed properly or the wrong mortar.
When that system gets installed properly believe me when I say you're not going to just pop off the old tile and install new. It normally comes up in big chunks with a demo hammer and a lot of sweat, tile, mortar, & ditra all still sandwiched together.