There are two assumptions between that claim that I don't think are proven: first, that a hostile environment in the tech industry can't have an indirect effect

There are two assumptions between that claim that I don't think are proven: first, that a hostile environment in the tech industry can't have an indirect effect on young women considering a career in tech; second, that the cohort taking the AP Computer Science test is a close reflection of the tech workforce, and that an attrition rate can be meaningfully derived between the two. The latter assumption in particular is one that I find highly dubious. This is only anecdotal, but I have noticed that many more of the women I meet in software started coding later in life than the men -- college or later. It's more likely to be a second or third career. Sometimes it was an aptitude discovered while working as non-technical staff at a software company. So an attempt to measure the effect of misogyny in the tech industry via attrition from AP Computer Science seems doomed from the start.