Yes, they are the owner and they can set the rules. But they can't ban you if you didn't break those rules. The players involved didn't. They tried to message the Devs through modern ways of contacting people, so the statement that they didn't report the "bug" is a lie. And the company is not allowed to act against their own rules. If they do, they have to compensate for any loss endured by their customer. Here they clearly acted against their own rules after they failed to protect dev constructions and/or places for the public community, something they have to do if they state that it is a safe area for anyone. And it that regard they are violating consumer protection laws in the combination with unruly bannings, because the players paid for the service the company allegedly provides.
As for any beta: It is normal to make glitches or exploits public. And this here wasn't even one of them, it was simply the devs fault not to lock editing-rights. As goes for that again: The company is not allowed to ban you for something you didn't do in their property, so making a permaban out of it because they posted it on reddit, is another act of consumer violation. It's like saying you are not allowed to buy in Walmart, because I heard you talking about how easy it is to steal there at the bus stop. It is not in their rights to act this way.