Yes, they proved Israel right. Israel was right that their actions, because of Hamas' predictably awful behavior, was going to lead to immense suffering for the population of Gaza.

How can Israel be right, and yet not at all culpable, unless they had no other credible choices?

Absolutely, Hamas is culpable. But culpability is not like pie. Hamas can be 100% culpable, in that they acting alone could have completely prevented the calamity; and yet Israel can still be culpable themselves to a large degree because they too could have greatly reduced the calamity and without dramatically increasing the risk to the IDF.