Couldn't hurt to test the hydrometer. Dunk it in 60° preferably distilled water. Should read 1.000.
The Grainfather looks like a pretty high tech (and price) gadget. I would think following the kit instructions the OG should turn out pretty close to the expected gravity listed.
How soon did you start to dump the sediment? The yeast will be in there too. I put two ports on my conical. One on the bottom to dump sediment and one on the side for samples or harvest yeast. I never touch the bottom one until I get my expected gravity or so. I test the samples from the side valve until I'm happy, drain from it until it's reasonably clear, then start to keg or bottle on rare occasions from it.