a us judge ruled that Twitter owns the tweets

Link? If it wasn't the US Supreme Court, then the ruling is significantly limited. And even if it was, that only applies to the US. Beyond that, we'd be getting into the nitty gritty of copyright law in specific jurisdictions - so far we've been talking about overall principles of copyright and intellectual property.

Twitter's current terms seem very clear on the matter:

You retain ownership and rights to any of your Content you post or share, and you provide us with a broad, royalty-free license to make your Content available to the rest of the world and to let others do the same.

You own the content, Twitter has a licence. They also provide no definition for "Content", so it can easily be argued that the username is content, as it is provided by the user.

Twitter can update their policy as much as they like, but it would ultimately be decided in the courts. Until then nothing is certain, but David doesn't always lose to Goliath, and courts don't like it when a big player is clearly taking advantage of the little guy. $50,000 value would definitely be considered.

More likely though there probably will be no legal battle. Twitter is circling the drain, by the time anything is heard in court they'll be gone. However that doesn't mean they should be allowed to do things like this with no objections.