Of course I don't mean that the database isn't reliable in that sense.

When I speak about reliability, I mean the extent to which the system tolerates a developer or user error. If a developer or user makes a mistake then a less reliable system ungracefully falls over. A reliable system catches the error as soon as possible.

One of the advantages of typing is that it catches garbage data earlier, when you try to assign a value of the wrong type. A typless system happily takes the data into the system, causing problems later.