I agree with you.
It was always assumed to mean "man". The American slang word "guy" means "man", at least in its native land.
Probably most operatic, "art", popular and pop songs ever written about love have assumed simple heterosexual romance, even if in illicit affairs, whatever their surrounding social attitudes towards other orientations.
This troll's notion seems symptomatic of a very modern trend to warp originally, rightly, well-intentioned drives for equality and tolerance of "difference", into dividing humanity into umpteen hermetic categories. Yet we are not database-indexed items in a vast warehouse - we are just people.
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Besides, the nine syllables of partner of unspecified gender would not rhyme with My.
Nor fit the two or three beats allotted to guy in the melody without squidging them into smaller fractions of a quaver than thought decent even for a Baroque harpsichord composition !
.....
Mary had a not-yet adult ovine whose fleece was as reflective of the resultant of the visible light spectrum, as snow.
And everywhere Mary went, the lamb of unspecified sex and unassigned gender was sure to choose of its own free will, to go.
Greensleeves is my delight.... (Very green: her/his clothes are of organically-grown linen dyed with sustainable vegetable extracts.)
