In the current episodes of Dragon Ball Super Supreme Kai seems to know Beerus well because they are connected and share the same life force so, if one dies, the other does as well. However, in the early episodes of Dragon Ball Super Supreme Kai seems to know little to nothing about Beerus, and the elder Kai has to explain who he is. Is this a plothole or am I misunderstanding the situation in this episode?
I think the explanation here is much simpler and Toriyama did not plan that much ahead (well at least it seems he did not develop a detailed story line). The manga is behind the anime storywise, and the anime writters seem to recieve just a general plot line (like characters and settings) but the interractions and story development is up to them to decide on it. That is why there are also so many differences between the manga and the anime, and that would also explain why at this moment the supreme kai knew so little about Beerus.
In the video, Kibito Kai clearly says that he is aware of who Lord Beerus is, when elder kai begins explaining it to him. But yes, he does seem to be naive about Lord Beerus' actions and nature.
Kibito's surprised emotion wasn't based on Lord Beerus his existence and role/power, but on the response and emotions that the elder Kai showed as he had never seen him "that afraid" before.
But then again, Kibito Kai has always been naive about many things since the time he was introduced in Majin Buu saga.