Two engineers placed side by side are never "equally qualified." Their competence will differ. If you look solely at their degrees and work history alone, you'd be ignoring the individual abilities of the engineers.
The parent comment to yours was poorly worded and snarky, so you have a right to be upset. But still, I think your reasoning is flawed. People are generally promoted by their competence and their negotiating/office politics skills, and you can't claim that those are the same across all genders. Why would women, who are fundamentally different than men, have the exact same competence and negotiating abilities as men? There's no reason the two genders should be equal.
If you really have two equally skilled engineers, one male, one female, and only the male is promoted, that's sexism. But two engineers are never the same, so you can't make that argument.