If you did a partial boil and topped off with water you could have gotten a bad hydrometer reading because the wort & water weren't mixed well. Other than that, I guess your hydrometer could be off or it stuck to the side of the tube and you just got a bad reading.
As an example, if you used a kit and added 1 lb. of DME to a 5 gallon batch you gained about 8.8 points, so if the kit was supposed to yield an OG of 1.062 a pound of LME would up it to about 1.071.
You did the right thing by repitching. Sorry I didn't catch the malt/grain bill part of your original post before my first reply.