This seems overly-cautious to me, too, but a few notes:
-a lot of folks have been talking about how they've run 5ks in similar or worse conditions in recent weeks. This race didnt cancel its 5k (or 10k); it only canceled its 10-mile.
-In my experience, women-focused races have more beginners than the female population at non-women-focused races (there are also other types of races for which that's true, such as ones with a strong charity tie-in, or untimed MOB events). If that's the case at this one, that may have played into TCIM's decision, knowing that their participants at this race would be less-prepared for and more taxes by the conditions than their other races (where they may not have canceled the 10-mile).
-That they had shorter-distance races that they could switch folks down to (and "make them whole" by offering a partial refund or discount to a future race) probably made the decision easier.
These factors, plus others, may have contributed to what appears to many of us from the outside to be an overly cautious decision.