If that's literally all he wrote, that sounds more like a polite way of saying "you're wrong, and I have better things to do than argue with you about it."

He wrote more than that. I no longer have emails from that period, so I can't quote his full reply. It was friendly, and seemed to engage with the point I was making.

Yea. "I suppose in some real sense"... What does that even mean?

That his book Consciousness Explained did not explain how there could be consciousness, but instead explained what we are conscious of. It's not that what the book does is not explaining consciousness, but it's only explaining it at a specific level, presupposing its existence and understandibility. Dennett was conceding that the explaining "the hard problem" was a real goal, and that his book did not tackle it.