While it's an idealized/toy setting, yes, these are both real categories of sensors. In particular, Sensor B, the "weird one", is just a system that has some defect/failure rate. An example might be a system that only works during the day and fails at night because it uses a camera. Or maybe a camera that's taking pictures from behind a helicopter rotor so it's frequently obstructed. Or maybe you are actually using a bunch of sensors and some of them are broken. (Of course, you'd have to tweak it a bit to get a scenario where every measurement is truly a 50% random split between meaningful and non meaningful, and you can't easily tell the difference, but as I said, this post is an idealized/toy setup.)

You could have some moving element with limit switches and an encoder, that’s pretty common. There’s probably others…

Normally the limit switch would be reliable but it will degrade over time, could be damaged in use, be assembled wrong etc… and the encoder might not be very accurate from the get go.

So if you want a safe/reliable system under as many conditions as possible you might get a problem space like this