We did not say that.
The quote these outlets are relying on appears in our March 2017 update, which is quoted here:
The DEFCON Warning System is not saying that. We are simply reporting what some other analysts are saying. It is our general policy not to make specific policy recommendations to national actors. We simply report on what is happening and offer an analysis on what it means or what can result from specific actions or movements.Additionally, some analysts are urging the United States to develop more low yield nuclear weapons for a limited war.
We hope this clarifies our position. Again, we make no specific recommendations ourselves.