Didn't Supreme Kai know Beerus in the early episodes? 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?

https://www.youtube.com/watch?v=oRWC1DsdQ8A
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.