In argentea, I find the females have more black coloring, and the profile less steep, more rounded, although individuals may differ. And non alpha males, will often mimic females.
below a pic of my alpha male to compare, note the steep, almost vertical profile, and very few black blotches.
Because of the body color, and gently sloped profile, it does look female to me....that being said, it's just 1 photo.
And sometimes without another argentea in the tank, a male won't show dominance characteristics.
Sorry to be wishy washy on this, but argentea are tricky to sex.
female left, male right, when they were younger.
note the extra mid body spots on the female and darker bands near the eyes. Also a slightly gentler profile