The coastline in Japan, as the MC mentions, has a disgustingly large amount of trash all over the beach; as does a lot of China, and India, honestly. I have heard that it can be a problem all across Asia, SEA, India, and many places around Africa.
(I think most people understand that throwing trash on the ground and walking/driving away is what causes this, so I won't belabour that point.)
So, yeah; that's a fair comment by the MC.
I'm glad that I live where we fine people $250 for any kind of litter for a first offense, and scale up the price from there.
Hell, people have even been sent to jail for it... and we still can find trash on the beach where I live.
Not much, but it's there.
So, finding No Trash on the beach, at all?
That would mean that either the island is insanely isolated (like Saint Helena), or there is no mass production and likely nothing beyond subsistence living where this body of water touches.
And if there is no form of disposable anything? Anywhere the Ocean has a shore?!
That is nearly caveman-level, like Neolithic levels of survival.
I'd be really heckin concerned.