While I do not know the exact context he said that, it does appear to be perfectly orthodox. He did not say we know all will be saved or that its even likely all will be saved, he said its reasonable to hope that all will be saved.
The Church has condemned the idea that hell is only a temporary purification but the Church does not say who is in hell or if anyone is in hell. The Scriptures teach that God desires all men to be saved and to come to the knowledge of the truth (1 Timothy 2:3-4). We also know that to die in a state of unrepentant mortal sin leads to hell, but can we say with certainty that any particular person died in such a condition?
Hell is indeed real and is a possibility, but whether someone or anyone is there is not something we can really answer. And given that God desires all men to be saved, it is not unreasonable to hope that all men be saved.