AFAICT the WFP budget is entirely separate from that of the UN, although they do get mostly contributions from governments. All WFP contributions are voluntary, none are 'due' or assessed (unlike for some other UN-linked organizations). OTOH that chapter mentions that WFP "Members are drawn from the UN system of state classifications." I'm not entirely sure what are the implications of that, if any.
So, what are the practical implications for the World Food Programme being "an international organization within the United Nations", as opposed some other food-oriented charity/NGO like World Central Kitchen or Oxfam etc.?