Over the years, I have heard many things about UNICEF, its management, and its policies that have made me regret the fundraising I did for them as a child.
Here is a link to their official position on adoption, including international adoption: https://www.unicef.org/media/media_41118.html. Given their actions, I believe the blog you posted is accurate in citing them as being anti-adoption. At the very least, their policies indicate that they believe that children should be raised in their country of birth, regardless of whether that is in their best interest or not. This is infuriating, given the number of times their official statement claims that "the best interest of the child" should be the determining factor.
How can anyone come to a reasoned determination that children separated from their parents by war are better raised in their home-country than in a safe, loving home far from the very danger that severed their family--just in case they might be reunited with a distant relative they might not even know?!?
The case of children separated from their parents and communities during war or natural disasters merits special mention. It cannot be assumed that such children have neither living parents nor relatives. Even if both their parents are dead, the chances of finding living relatives, a community and home to return to after the conflict subsides exist. Thus, such children should not be considered for inter-country adoption, and family tracing should be the priority. This position is shared by UNICEF, UNHCR, the International Confederation of the Red Cross, and international NGOs such as the Save the Children Alliance.