I don't know why you call him dumb. In his situation there are few ways to verify that Japan had indeed surrendered. If it really was an elaborate scheme by the Allied troops then he would have been called dumb for surrendering so easily.
His belief that the Allies would go through so much trouble to stop a group of people who had killed relatively few people over a 30 year period is what makes him dumb.
What troop movements was he observing? What logistics was he disrupting? How effective could he possibly be gathering intelligence if he couldn't even report his findings to his superiors? Even if the war was still going, his contribution to the war effort was minimal compared to the effort the Allies appeared to be putting forth to "capture" him.
Hiroo Onoda may be dumb, but I believe you can't tell that based on this story. To suggest otherwise is myopic.
Apply Occam's razor: news of Japan's surrender is a (probably not uncommon) Allied trick vs. the US created a magic secret weapon that would force Japan -- a country so dedicated to winning they crash planes into boats -- to surrender shortly after Hiroo left it.
In Hiroo's Japanse solider's shoes, which seems more likely?
So, true, you'd think he'd eventually figure it out (i.e. give up), but perhaps his grip on reality became a skewed after living alone in a jungle for decades (i.e. he's made of tougher mettle than I am).
Still doesn't indicate dumb to me though.
(Edit: Added epiphanic id ests to last paragraph.)
In 1946, perhaps, in 1950? 1955? 1960? 1970? no. At that point, 5, 10, 15, 30 years after the fact the idea that Japan had not lost the war, the war was still going, and yet they had not reconquered the Phillippines doesn't pass the smell test.
I think we have to question if Onada really still thought in days, weeks or years. At least to me, it does not sound totally unbelieveable that he eventually stopped counting days and weeks and rather lived a sequence of days. A very long sequence of days, long enough to make him lose track how long it was.
At least to me, this is kind of plausible, because he had no more reference in his days. You know: Hey, every seven days there is this special day where I cannot go shopping if I need something. This coincides with a week going by, and thus, you have a fairly "natural" notion of a week. For him, I guess, a day consisted of getting up, checking his surroundings, gathering intelligence, staying hidden, maintaining his weapons and eventually hiding and going to sleep again. Day after day after day.
I think extreme isolation can lead one to believe anything... even in the face of all those facts. The human mind is an elaborate machine and will comfort you in the strangest ways.
