The Global has mentioned that YouTube is not fully blocked but ironically just part of it without declaring any reason to partially blocking it.
“Sorry, this page has been blocked by National Telecommunication Corporation.”
Yet, it is not clear if the authority is really censoring it or not, however, some users are able to access YouTube without experiencing any issue as they said in the article. It seems that some of the ISP are implementing the blockage (“According to the source”) and rest are in the way which explains the previous statement.
The interesting part of the action is why don’t they explain their goal of blocking such a website. Lack of communication could increase the gap between the two parties. Personally, I could say it is individual acts either high or low official came up with blocking this site.