http://www.worldvision.org/our-impact/our-faith-in-action
It does not appear that there is any official direction to NOT preach the gospel, so not sure how accurate your understanding is.
They used to preach the Gospel but no longer do.
Now they believe that people seeing good things done is enough.
https://blog.worldvision.org/conversations/qa-witnessing-to-christ-through-our-work
Do we preach the Gospel to non-believers? If not, in what other ways do we witness to our faith?
Bryant Myers, one of the great thinkers for World Vision, used to say that our work in development provokes the questions to which the Gospel is the answer. Isnt that an amazing thought? We witness by our life and our deeds as individuals, through the signs of Gods action, and by word when people ask the question. Good development, which says that injustice and inequality are unacceptable and reparable, makes people ask these questions from a place of openness and freedom: Why do you stay after the war breaks out and others leave? Why didnt you let us stone the man who stole that money from you? Why do you ask about my children and care about me?
Some define proclaiming Christ narrowly, as a spoken call to repentance preached to large groups. But God has opened doors for World Vision to work in areas where certain methods may be inappropriate and insensitive or ineffective. Jesus gives us an example to follow. By feeding the hungry, restoring sight to the blind, and freeing the oppressed, He showed that His Good News includes the promise of care and hope for the downtrodden. Following in Jesus footsteps, we proclaim the hope of the Gospel not only in words, but through the quality and character of our lives and by our actions on behalf of others.