There is a difference between a man leaving his diaries , which would have revealed his sexual orientation albeit an open secret within his close circle , and the recipient of those diaries using them as a tool to market his home to visitors.
The donor could have reasonably expected the first but not the second.The fact Is that he was a very interesting and accomplished man who happened to be gay , not that he was a gay person full stop.
The film may show that he was an interesting man but the NT would not have made the film were it not for the fact that they wished to run a marketing and publicity campaign piggy backing on the anniversary of homosexuality ceasing to be a criminal offence .I think this is rather offensive actually , they are using this aspect of his life to make money, and I would hazard a guess that the donor would have been pretty surprised to find that his sexuality was being used by the trust in this way albeit he probably knew that leaving his diaries to the Trust would have revealed his sexual orientaton..