While I have no more information on this hack than my friends enthusiastically sharing the news: it seems Don Jr.'s account for making the brilliant Tweets was compromised. The hackers, in using Don Jr.'s account to convey a message that was patently untrue and in poor taste, were quickly able to fool people into thinking it was real.
The social media post was taken down, however, it did previously live at this URL: https://twitter.com/DonaldJTrumpJr/status/1704471798622921153
I find it a horrible joke that Junior might run for office, and modern rules of comedy should bar such claims. Also, you'd think the Trump family's expert social media people would be able to help them set up 2FA already.