Posted another link elsewhere that explains the ambiguous terminology a bit:

https://projectnettie.wordpress.com/

Although rare, some individuals have disorders of sex development (also referred to as intersex conditions). Most of these disorders are male or female specific and do not cause ambiguous biological sex. Some individuals have reproductive anatomies with both male and female features; here, biological sex classification is a complex process with input from medical professionals and parents. Not one of these individuals represents an additional sex class.

I think the answer you're looking for is that ambiguous is being used in the sense of "not immediately obvious, requires further investigation", not "impossible to know in principle"

Either way, thanks for the conversation (and pedantry!)