They may know that, but it is irrelevant. English lacks the phoneme /x/ and the usual substitution in assimilating foreign words (or the letter-play that Donald Knuth started with TeX) is the closest unvoiced velar that English has: /k/. See how most English speakers pronounce the name of J. S. Bach as [bak], with only a small number of pedants saying [bax]. Or, outside of Scotland, Loch Ness is usually [lɔk], not [lɔx].