It's not known what happened at this point: The Twitch channel was completely gone for a while, but is currently back though offline (the viewers are expressing their displeasure in a very Twitch-like fashion) while the hacked tweets have been deleted and the account cleaned up.
The hack also reportedly impacted his personal Twitter account, which for now still has a few tweets that may or may not be from the perpetrator—they're relatively innocuous (at least compared to the ones above) but also have a certain graffiti-like styling to them. The fact that Beahm hasn't tweeted from that account since late 2017 is probably telling, too.
Some of the tweets are a bit funny from the outside, but the hacks reflect the darker side of internet celebrity status, which comes with unprecedented levels of perceived accessibility to fans and a lot of line-crossing. That typically results in things like like stream spam or personal attacks on social media, but it can also lead to privacy breaches like this and more serious threats: DrDisrespect's house was shot at with a BB gun last year, and others have been subjected to very dangerous swatting.
It's also a reminder that two-factor authentication, while sometimes a pain in the ass, is essential. No system is perfect (and I would guess that DrDisrespect has 2FA enabled across the board, so how all three accounts were compromised simultaneously is unclear for now) but even if you're not a high-profile streamer, your odds of avoiding nonsense like this are a lot better with it than without.