I came back an hour later to find an old lady, having occupied my former spot, waiting a while to see if the owner returned before taking it to the nearby police box. I was all over myself apologizing and thanking her in my crappy Japanese, but she didn't get what I perceived as abnormal about the situation. She didn't even take me up on my offer of a baked sweet potato.
Another time, I accidentally sprayed 500 yen (so, roughly $5) coins all over the floor at Comiket when trying to extract change from pocket. Being Comiket, a coin rolling a few meters may as well have been a mile off due to the sheer crush of bodies. Since I was at the head of the line and didn't want to inconvenience everyone behind me, I mentally wrote them off as a loss and continued buying my hen^Wartbooks, only to have all the coins immediately returned by a guy who saw what had happened and went scrambling around for them. He, too, refused all thanks and melted back into the crowd.
So, although I can't attest to the laptop thing, it definitely wouldn't surprise me. The similar anecdotes in this thread seem to agree.
https://www.nationmaster.com/country-info/compare/Japan/Unit...
https://medium.com/@alascii/this-guy-left-a-laptop-in-a-toky...
https://www.attendly.com/the-astonishing-lost-and-found-cult...
https://japantoday.com/category/features/kuchikomi/japan-a-g...
https://livejapan.com/en/in-tokyo/in-pref-tokyo/in-tokyo_tra...
(Of course, whatever Japanese culture might be, Japan now also has millions of tourists each year, with whom, YMMV).
Been bicycling daily here for 10 years, never lock my bike. It's been stolen once, but with a bike costing <$100 I figure I'd rather save the 10 seconds per day vs. not losing one bike per ten years.
Forgot an iPhone once on a bench outside. Person who found it immediately called my contacts to find out how to return it.
Dropped my wallet once in Tokyo. It was returned to the nearest police box in less than an hour.
My friend lost her passport in Kyoto, it turned up at the lost and found. Peering in through the window they had a little bit of everything, and roughly a million umbrellas.
In Canada I just assume anything not bolted down will get stolen. I left company laptop on a taxi before and it got stolen, even so I called the taxi company 2 mins after.. lol one of the many reason I have no problem with Uber screwing cabbies.