Like with a lot of lefty causes, they seek to redefine a word — in this case “gender” — in a way that suit them politically. The redefinition will then allows to apply the old values attached to the word to the new groups covered by the word. Like they did with “marriage.”
Here they are trying to redefine “gender” from its original genetic meaning of male or female (yes, chromosomes are either male or female, or very occasionally there is a defect), to mean the huge variety of categories of sexual attraction. Not much harm in that, one might say, it’s just semantics. People are tricked into saying “yes” at this point. The problems come when they then try to apply the rules and customs around genetic gender to the new meaning of types of sexual attraction. Uh oh.
Of course, the ABC is a very left, PC organization. They ran or paid for the survey, so who knows how biased they were in choosing respondents. They are just as likely to use surveys like this to subtly push their views, by persuading you that lots of people are changing to the ABC’s viewpoint. So you can be reasonably sure that the number who believe there are more than two genders isn’t any more than they present here.