Disbelief might be a stretch, but he is clearly extremely excited about the recent advancements and proud of what the team has been able to accomplish.
I agree that it's fun to witness that level of passion and it makes me happy that Chris is so amped about this.
Small plug for an OSS project my coworker started: Colonel Kurtz: a Block-based content editor. It's absolutely not a "batteries-included" sort of thing but if you're looking for more of a lower-level library with which to build out a custom block-based editor then this is right up your alley.
I agree that it's fun to witness that level of passion and it makes me happy that Chris is so amped about this.