I don't think they're explaining everything they're doing in that post. I'm assuming they're doing a combination of what I suggested here, http://geek.ryanhellyer.net/2014/06/04/spam-epiphany/. With the addition of a non text-based CAPTCHA as a fallback. But they're still using text-based CAPTCHA's too sometimes, since those are still more powerful than those image based ones since you can't just take a potshot guess at the answer since there are too many combinations to choose from.

I'm sure this is an improved implementation for them, but it is not revolutionary. In fact I'm running a test version of this exact type of setup (not identical of course) on my own site right now, with the exception that I haven't implemented a non-text based CAPTCHA fallback. This will eventually be rolled into my Spam Destroyer plugin once I've ironed out the bugs and added a few more features to it.