Infer reasons Detering may have picked the cherry blossom and left camp.

I would infer that the cherry tree reminded Dettering of home. Once he saw it, he decided to leave. Text evidence provided below.

"Surely I can pick cherry blossom if I want to!" he replied evasively--and after a while: "I have a big orchard with cherry trees at home. When they are in blossom, from the hay loft they look like one single sheet, so white. It is just the time."