The meaning was not simply open and freely given to all. It was that plus a payload of a specific type of condemnation of historical villains that is fundamental to the current campus dogma. The meaning of "made available to the public" is not one of the dictionary senses of the term "decolonized", which caused the "confusion" mentioned by the questioner. The "open" part of the meaning as well as the full implication can only be parsed if you recognize the doctrinal jargon.