Let's say we believe that women are on average equally as capable of men, and we know there are maybe 10-20% as many women in the industry.
Are those 10-20% women roughly as good as the average man, or are they roughly as good as the top 10-20% of men? Have they had the same experience as average men, or have they fought through and survived discriminatory barriers?
Even if we suppose the answer is somewhere in-between, it wouldn't be surprising that women are highly sought-after. Because with these assumptions, the women in the industry are generally likely to be better on average.
Maybe we don't observe discrimination against women in this specific context* (post-application and pre-salary negotiation), but that doesn't mean it isn't occurring elsewhere.
*The summary data includes non-technical hires at tech companies