Tyre oddity...

[DCBassman]

This just caught my eye on the Trek.

The tyres are Schwalbe City Jet tanwalls. The size is 26x1.95. Or, the size is 54-559. 54mm = 2.1", and at an eyeball guesstimate, I'll go for 2.1.
How did that happen, then?

 

[Milkfloat]

Over the years I have seen all sorts of strange figures on tyres, I sometimes think the manufacturers just guess or even put on random values.