Do they? Japanese has no distinct plural form, the plural is identical to the singular. I'm not familiar with any literary uses off the top of my head of 神 where it's unambiguously singular but referring to anything other than the Christian God or a specific spirit. And even if that were so I don't think it necessarily means very much. Greek uses ὁ θεός in the singular all the time without direct reference to a specific god, either because it doesn't matter or its clear enough. After all, what is θεὰ in μῆνιν ἄειδε θεὰ Πηληϊάδεω Ἀχιλῆο, the first line of the Iliad? It's clear enough but it's supposed to be the muse, but there's nothing there that actually says so.