If she applied after him getting his application approved, this might very well explain her tiny line of credit: the algorithm didn't look at him and her alone

If she applied after him getting his application approved, this might very well explain her tiny line of credit: the algorithm didn't look at him and her alone in isolation, but at both at the same time, saw a certain combined income, saw he already has a large line of credit issued and concluded "I am not giving them another 3000 bucks or whatever, they already got that, so let it be 50 bucks or something, the minimum we can give to a customer, because really they together used all the credit we're willing to extend already when he got his card approved". If she applied first, she might have gotten the big chunk, and he might have ended up with the tiny chunk. Or it might be that the algorithm training data was just biased against women, which is entirely possible as well. The black-box-ness, even to employees, of course, is a huge problem.