First time I saw geohashing. Can't this result in some lopsided squares? The way it is described has a standard rectangle projection. But those are inaccurate due to the earth being spherical. So the areas on top and bottom will be much larger.

To be fair I've heard of most of these in my career but they are fairly specialized. If you are conducting a system design interview and expecting the candidate to know one of these I'd suspect there is a bit of bias there (unless that is their area of study).