Single-user, a single natural person, doesn't striclty mean single-accessor though. I don't think anyone here is suggesting that sqlite is a viable replacement a for any networked client/server postgresql system, but it is certainly capable of handling more than the most basic 1:1 tasks. Beyond that, the point is that you only need a file, so when you have natural data boundaries, a lot of problems decompose to that single user/single concern paradigm.

'production' doesn't equal 'multi-user concurrent access'. There are production uses where sqlite is a valid choice even if it may not be the best choice for multi-user production use cases.