To be honest I don't see a disconnect at all between the two - both address the fact that any relationship outside God's will is wrong. One is written from the point of view of singlehood - the other from the point of view of marriage.
I never did see where Mohler encouraged marriage outside God's will - he expresses his concern that many are not heeding God's call to marriage...
I do believe some are called to be single - we have a fellow in church in this situation - so far in his life it's apparent that he's not been called to marriage.. it doesn't affect his ability to serve in our local church ...