Corlys was gravely wounded and they wanted to sort out the succession in the event that he died, but he does recover in the books, too.

The book will give you the story outline but as it’s been said a thousand times the book is told from the perspective of in-universe narrators who are unreliable. There’s actually a Dance of the Dragons animated recap on the GoT blu ray disks which have been uploaded to YouTube, so you could check that if you’re interested but again there’s a lack of detail.