I know some folk will defend anything DB says, but he clearly claimed the expansions were free, there is no amibiguity in that statement.
Edit full paragraph added so context is clear:
"
I think we were the first open-world space game, there were no other open-world space games when we commissioned the game and went to kickstarter. Being first was good, we have a very loyal following, we’ve added new content to the game continuously since it shipped. Our expansions have been free, and the things you pay for are just vanity items, which in a multiplayer game just makes sense. I think that’s worked well, and it’s that loyal fanbase, and the fact that there’s lots of things in the game for people to discover. We had aliens in the game and we didn’t announce them, we just let people discover them, and there was a lot of buzz around that."