Haven't noticed that difference, the languages I did this kata in had that example and I assumed they were consistent. Changed the description so all languages have the moOse example now.

The example in the description shows what "ignore letter case" means:

isIsogram("moOse") == false // -- ignore letter case

An isogram is a word that has no repeating letters, consecutive or non-consecutive.

There are two o in "moOse" (ignoring letter case they're equal).