Now that's a blast from the past in typing class. I remember hearing people complaining about this or rather using it as a horror story about the class. Of course by the point in the class you use these, you've passed the point of being expected to know where the keys are and it is pretty much an advanced part of the class.
A not insignificant number of keyboard enthusiasts prefer to use blank keycaps. It's often merely an aesthetic choice, but those who like to tinker with custom layouts also favor them because that lets them skip shuffling keycaps around following a layout change.
The last stage of mastery is when you drop the need to prove to the world that you don't need to shuffle keycaps by just keeping the existing ones rather than blanking them out.
Back in the dark ages of having to work in an office with shared space in a cubicle farm, it wasn't unheard of where people would swap their keyboards with others because theirs was not working correctly rather than going through IT to get it looked at--possibly also knowing IT might just shrug their useless shoulders at it. I'm guessing a keyboard with blank keys would prevent that.
You know, it occurs to me that musical instruments have blank actuators (keys, fingerboards, valves, ...); yet that alone doesn't prevent music learners from staring at their hands while playing, and that's a habit that can persist for years or decades even.
People learning typing on computers should be encouraged to keep their eyes where their typing appears on the screen.
Not sure if that's your reference or not???