I as well. It wasn't a TOTAL giveaway as she used bits of Tim's pod to build it, so the tech is in there, and The Doctor's built all sorts of stuff out of local (and often non-technological) technology. The speed with which she did it is a bit suspect, but it didn't really take me out of the story. The doctor has been seeing doing things at speed on occasion, so it's hardly out of the blue.
In any case, the Doctor has never been seen to build a sonic. The last two were literally created for him by the TARDIS, and it's unknown just what input he had in its construction. Heck, one could argue that he built the function into the TARDIS in the first place, to save the time and trouble of firing up a double flamethrower every time.
Mark