The guidance refers to sex registered at birth, not legal sex.
Also, it is guidance, not a regulation, so is intended to illustrate and illuminate, not provide every possible example of an offence. In the end, it's the court which decides whether sex has been obtained by deception or not, which could depend on how well the case is presented.
There's some wild case law around this, such as the Arab Israeli jailed for having (casual, consensual) sex with a Jewish Israeli woman without mentioning that he was not Jewish.
And in England, this case:
https://www.herts.police.uk/news/hertfordshire/news/2024/may-2024/bishops-stortford-man-jailed-for-sexual-offences/
(The offender was dressed as a woman and the victim was very drunk.)
Also, what @Hoardasurass and @JanesLittleGirl said.