I'm not a fan of Cillian or Kylian particularly, but I certainly would have known to pronounce them both as 'Killian'. A quick Google shows that there are lots of spelling variants of this name, going back a long way, many of them starting with a 'k'. In fact, Wikipedia says the name originated from St Kilian, an Irish missionary to Germany in the 7th Century. Pronouncing the beginning of Kylian as 'Ki', not 'Kye' is surely hardly surprising. It's pronounced like the 'y' in Dylan or Lynn. The 'Kylian' variant is pretty popular in France. People on MN do love to jump to conclusions about names though.