The "harassment" part makes sense at least.
> and it related to the claimant’s sex
I'd have assumed "sexual" meant relating to sex (intercourse), rather than relating to sexes (male/female).
I think the relevant act would be: https://www.legislation.gov.uk/ukpga/2010/15/section/26
No, sexual harassment is any form of it that references the sexes (male/female), otherwise garden variety misogyny (e.g. "women are bad at X", "X is bad at Y, because she's a woman") wouldn't be considered sexual harassment.
Misogyny is not identical to sexual harassment, they are two different things with some overlap.
EDIT: would downvoters (or downvoter + socks) like to explain their disagreement? I'm happy to be corrected.