That was a recent addition to the Terms. What that is referring to is additional DLC once the game is complete. Right now it is in beta. If you own a alpha license, you are guaranteed to receive additional updates free. The idea was that they were afraid of a "Everything in the future is free" clause, so just in case; they added that. There is currently no planned 'bonus updates'
The clause I quoted was there even during alpha (unfortunately web.archive.org doesn't have older versions so I can't link it).
During alpha the rules were: "if they release updates, you get them for free. But you agree that when you pay, you pay for the game as-is and you don't have any right to expect updates".
Meaning: "Maybe I lose interest in doing this and just stop updating it. You have no right to be mad about this. If I update it though, you will get that update for free"
