Atlantico website (more or less extremist) says it is due to the qatari representative who is a terrorist. Their opinion, because i am not sure it's true.
Ah the Gulf states geo-politics has made it to UNESCO as well.
Qatar is being painted as the funder of all evil by its neighbours at the moment, so not a surprise UNESCO is being pulled into it too. There is plenty out there about the breakdown in relations in the Gulf but this podcast episode from Planet Money
gives a good run-down on it.
I'm not suggesting that Qatar is innocent of what it is charged with, however it is worth bearing in mind this geo-poltical game being played if you see anything negative about Qatar (or their hosting of the 2022 World Cup/ dealings with Paris Saint-Germain football club etc) in the next few months.