The survey is of academics across all disciplines so there is no particularly good reason to treat their views on the topic with particular importance.
There’s also this:
58 per cent of respondents think sex is binary, except in rare cases such as intersex individuals
So they’re only saying it’s mostly binary.
(Censuswide, who ran the survey, as are members of the British Polling Council so we can at least expect them to have run the survey reasonably.)