"It’s an inherent technical problem down to the fact that females generally have higher pitched voices. They also tend to be quieter and sound more “breathy”."
So in other words, women can't speak as clearly as men, on average. It's like saying facial recognition programs have trouble with black faces because they scatter less light, so in training that's fine because there's a big spotlight, but in real life it doesn't work as well, and can never work as well.
This beautifully complements an article in The Guardian the other day that stated that algorithms favour white men because there aren't enough female coders, along with a lot more idiotic garbage.