While I'm sure this would be true by any metric with Trump it seems odd that this is just a simple look at medians. I thought pay gap referred to the gap between genders for the same/similar positions
No, generally pay gap looks at broad averages as well. Which seems counterintuitive, and certainly undermines the "equal pay for equal work" slogan (the pay gap for equal work is only 8% or so, compared to the general pay gap of 25%), but doing the math this way brings out a lot of the subtle sexism that can have wide-reaching effects.
If women in general have a harder time getting hired for senior positions, or if they're systemically discouraged from even seeking such careers, or if female-dominated careers are, for no apparent reason, less valued than male-dominated careers: those are all problems.
Unfortunately sexism in the real world isn't as simple as moustache-twirling fat cats cackling as they sign smaller checks for women. But it's still real.