I'm sure the ACA had absolutely nothing whatsoever to do with this. Nothing at all.

Full Disclosure: The Robert Wood Johnson Foundation has long-term paid banner ads on this website.

Having said that, I don't think anyone would disagree that the RWJF is a pretty reliable source for this sort of national healthcare data analysis:

The Widespread Slowdown in Health Spending Growth Implications for Future Spending Projections and the Cost of the Affordable Care Act

The United States is on track to spend $2.6 trillion less on health care between 2014 and 2019, compared to initial projections made right after the 2010 passage of the Affordable Care Act (ACA).

The Issue 

• The report uses health expenditure data produced by the Centers for Medicare and Medicaid Services and consistently adjusts in each year for the absence of the sustainable growth rate system for physician payment rates in Medicare.

Key Findings

• The United States could spend $2.6 trillion less on health care between 2014 and 2019.
• The authors note that despite signs of spiking health spending in 2014, there is evidence that spending growth has slowed down again.

Conclusion

• The authors identify several possible causes in the projected drop in national health spending, including the effects of the Supreme Court’s ACA decisions and sequestration in the Budget Control Act of 2011, as well as the recession and the subsequent sluggish economic recovery.

I'm kind of swamped, so I'm gonna leave it at that, but read the full report. Fascinating stuff.