Alexander believes a lot of things. But you can just look up the stats on STEM fields yourself; they're not hard to find. There are STEM fields that approach parity, there are a couple in which women slightly lead men, and there are a bunch with more men than women. But CS is, by what to a casual glance looks like multiple stddevs, worse than the rest.
Unless math is "warmer" than CS --- it isn't --- this explanation doesn't hold much water.
Unless math is "warmer" than CS --- it isn't --- this explanation doesn't hold much water.