It says the estimates skew greater for younger people and women responding. Well are younger people and women more likely to know which of their friends are LGBT, because of a host of societal reasons that tend to influence men or older folks to wall off their feelings and communicate less about such things?
I'm just saying, having lived in more than a dozen locations in five states and a Canadian province for the past several decades, the 4.5% number feels low to me (as in, impossibly so).