1. He was speaking to a receptive audience. The head nods when he starts to make the comparison between the energy for bringing a human up to speed versus that for training an AI.
2. He is trying to rebut a _specific_ argument against his product, that it takes even more energy to do a task than a human does, once its training is priced in. He thinks that this is a fair comparison. The _fact_ that he thinks that this is a fair comparison is why I think it is too generous to say that this is just an offhand comment. Putting an LLM on an equal footing with a human, as if an LLM should have the same rights to the Earth as we do, is anti-human.
It also contains a rather glaring logical flaw that I would hope someone as intelligent as Altman should see. The human will be here anyway.