Raw data here: https://d3nkl3psvxxpe9.cloudfront.net/documents/YouGov_-__LG_B_and_T_perceptions_LGBTQplus_sample.pdf

sample group is 1,023 LGBTQ+ Britons age 16+

I have to assume that means the "heterosexual" category is either all hetero trans people or people who just lied to get into the survey for some reason?