It seems this stems from which agency controls which maximum. For HSA limits the IRS is in control, for ACA compatible plan limits Health & Human Services (HHS) is in control. The IRS issued guidance in around May of 2015 including the upper limit of $13,100 for 2016, and in August HHS was more aggressive with the upper limits resulting in the $13,700 level you're seeing.
My speculation about catastrophic plans is irrelevant. Though you could speculate that the deviance of these two maximums is the result of a difference in objective between the two agencies. The IRS "loses" billions in tax revenue each year to tax-exempt vehicles related to healthcare (employer cafeteria plans, FSA, HSA, etc.) and may be seeking more modesty related to increases while HHS wants the most number of healthcare enrolled citizens (higher maximums can stem premium increases).