It's most likely the sediment that caused the high reading, if the hydrometer is otherwise calibrated and you have corrected for temperature. It's widely believed that the hydrometer is not affected by suspended sediment - but in fact it is:

> Hydrometer analysis begins after thoroughly mixing the sediment and
> water, after which particles settle out of the water column according
> to Stokes’s law. The density of a sediment-water suspension depends on
> the concentration and specific gravity of the sediments present in the
> mixture. If the suspension is allowed to stand, particles will settle
> out of the suspension and the density of the sediment-water suspension
> will decrease. A hydrometer measures the density of the suspension at
> a known depth below the surface.

Although this is discussing [drilling][1], the same principles apply. While the solids are in suspension, the density of the liquid/solid mixture is the average of the liquid and solid densities.

It's not possible to determine what the original gravity was without knowing the average density of the sediment in the sample jar. 

Just chalk this one up to experience - no real harm done. Next time leave the gravity sample to settle and also to settle to room temperature, so the hydrometer reading is accurate. 


  [1]: http://publications.iodp.org/proceedings/308/205/205_4.htm