You can tell from his expression in panel four that the Captain does not want to be the one who has to tell Rune that his entire extended family is dead.

Rune was going to see his uncle because he was the Head of House Beowald in Rune’s absence, and would have been able to fill Rune in on the political situation. Rune does not want to walk into the castle uninformed, because he doesn’t trust Lord Redley (his regent and Justin’s father) to tell him the truth.