"In spring this year my life changed massively when I met someone, and they make me feel so happy, so safe and everything just feels great," Daley said. "That someone is a guy."
His use of "they" for the first reference to his new romantic interest has "someone" as its antecedent, and rather than being a bound variable semantically (as in Everyone should look after their own gear), it's just a free pronoun meaning "he or she, as the context may dictate". He could have used he, as typical conservative usage advice books would have insisted. Except that it would have utterly ruined his rhetorical design.
That design (as pointed out by Ben Zimmer) was that he wanted the "big reveal" about dating a male to come at the end of the of the two-sentence paragraph, rather than be revealed by a pronoun choice early on.
P.S. Naturally, Daley's charming and praiseworthy openness about his love life prompted hundreds of fat, ugly, bitter, twisted, repressed, inadequate people to attack him in abusive fag-hating tweets. Thank you, homophobes everywhere, for continuing to come up with brand new ways to persuade me that my policy of not opening comments is a winner! Please use Twitter for your attacks; Language Log chooses not to be available to you right now.