So /live is some kind of a redirect to whatever other stream source. My guess is that whoever was meant to post the latest stream had this guy's URL in his clipboard history. Oops! Hard to see it being hacking - there are way more "interesting" things to do if you have the keys to whitehouse.gov - and it's not really a big deal, except for the poor schmuck who was watching personal finance videos at work, and maybe to the guy who just found out he has a fan in the Whitehouse. Hope neither of them gets too much federal law enforcement attention.
A decade later, I was responsible for securing systems in the same type of environment. Various incidents demonstrated that these types of compromises are easier than you might imagine.
Infosec of US government networks changes less over the years than senior leadership would have you believe.