In bed on phone, but what happens if
x = 3
[f(x) for f(x) in (sin(x^2), cos(x^2), tan(x^2))]
?
Half not expecting that to work, but it could be imagined. More likely explanation is just that f(x) = 3 is a valid variable (and function) assignment, so it happily loops through.
[f(x) for f(y) in 1:3]
Is probably less opaque.