Why was it said about Sad ibn Muadh: "If anyone were to escape the compression of the grave, Sad ibn Muadh would have escaped it"?

The Prophet, peace and blessings be upon him, said: "Had anyone been spared the compression of the grave, Sa'd ibn Mu'adh would have been spared. Indeed, he was compressed once, then released." The meaning is that Allah has decreed the compression of the grave for every deceased, and had anyone been spared it, Sa'd ibn Mu'adh would have been, due to his high status in Islam and his jihad. Indeed, the Throne shook at his death.