....he didn't say he was wrong. He said it was a possibility.
Look, we don't know for certain who perpetrated it. But look at what we do know. No Hamas rocket has ever caused anywhere close to the level of damage done to that hospital before. And on the other hand, the hospital director said the IDF had already fired two mortar shells at the building before, as a "warning". Then we have the fact that the IDF has already bombed numerous hospitals in Gaza. And to top it off, an active in-field member of the IDF tweeted that they did it, before deleting it.
Against that, we have... uhrm, just the IDF denial and the US gov (who don't have investigators on the ground) agreeing. Which don't mean much since we have on-record, acknowledged instances of the IDF denying similar stuff they were proved to have done, such as the bombing of Beit Hanoun elementary school.
The balance of probability very clearly points to the IDF. It ain't certain-- there's the outside chance of a rocket misfiring and then igniting car fuel tanks. But I'm going with the scenario that has already happened numerous times before as the likelier option: the IDF bombing a hospital and then denying it.