The paid for tiers on nodebbs website are for people that don't want to install, configure and maintain themselves.
Yeah, its still free. I wish they'd use the NodeBB.org domain for more of the open source community side of things, and use nodebb.com for the commercial side like wordpress does. But alas, they need to make a living somehow...
They charge for hosting services. But NodeBB is open source just like it used to be.