Perception: Dad confirmed that he understood the message, then said “cool”, then made some weird joke.

Context: assuming this was really the first time when Dad heard the news.

Interpretation: Dad’s reaction is just the beginning of acceptance. More reactions are to come. In order to really accept such a serious news, his emotions must go through all the “stages of grief” (even this isn’t exactly a sad news - but the stages are similar) en.m.wikipedia.org/wiki/grief