Did The Judge Err?

In his NYTimes op-ed, Richard Goldstone wrote:

Repeatedly, the Israel Defense Forces failed to adequately distinguish between combatants and civilians, as the laws of war strictly require.

What does the Geneva Convention say:

Article 51: Protection of the Civilian Population

1. The civilian population and individual civilians shall enjoy general protection against dangers arising from military operations. To give effect to this protection, the following rules, which are additional to other applicable rules of international law, shall be observed in all circumstances.
2. The civilian population as such, as well as individual civilians, shall not be the object of attack...
4. Indiscriminate attacks are prohibited...
6. Attacks against the civilian population or civilians by way of reprisals are prohibited.
7. The presence or movements of the civilian population or individual civilians shall not be used to render certain points or areas immune from military operations, in particular in attempts to shield military objectives from attacks or to shield, favor or impede military operations. The Parties to the conflict shall not direct the movement of the civilian population or individual civilians in order to attempt to shield military objectives from attacks or to shield military operations.
8. Any violation of these prohibitions shall not release the Parties to the conflict from their legal obligations with respect to the civilian population and civilians, including the obligation to take the precautionary measures provided for in Article 57.

And moreover, as I was told, "neither Goldstone nor the NGOs whose claims he has copied, know how many “civilians” died, have any idea whether the attacks on “legitimate military targets” were “disproportionate”, whether “hospitals and other civilian structures” were used by Hamas, and whether “precision weapons like missiles from aerial drones” were used".