I assume he means although the stigma is much less than it once used to be, it's not especially culturally acceptable for a woman to conceive a child from a man who isn't her life partner. Most women who do, do so by accident.

Also, while the man is out at war, the woman usually won't be procreating with anyone else until the man dies. The news of his death will probably affect her badly, and procreation is probably the last thing on her mind at least for a while (after which she may be too old).

But yes, hard data would be even better.