I cannot access the paper, but in the introduction it also says that only 40% of new members are women. The most likely conclusion is probably a convex combina

I cannot access the paper, but in the introduction it also says that only 40% of new members are women. The most likely conclusion is probably a convex combination of 1. Most of the time it is quite clear who is the best candidate and no gender-based tie-breaker is required 2. Publication- and citation records (which anyway are a lousy measure for scientific merit) are very heavily gender-biased (this was asserted in another comment) 3. The AAAS and the NAS use saner criteria than those publication- and citation records. My guess would be that 3. has the highest weight of these.