I like it because it's such a passing, no-big-deal moment which the novel doesn't treat as odd or in need of explanation.

ETA: it's very distinct from the gatekeeping (or pleading-with-gatekeepers) picture of transfem experience which goes "well she's really a Normal Womanly Woman trapped in the body of a man, so naturally she will exclusively be sexually attracted to Normal Manly Men" -- Fay generally is only attracted to butch cis men, but occasionally her attraction to masculinity means she'll glance at someone else too, and the book doesn't feel the need to tidy that out of the way so as to insist her desire is exclusively "straight."