The U.S. reduced carbon emissions by over 40 million tonnes last year, more than any other country. On a percentage change basis, however, the U.S. fell outside the top 20 for emissions reductions in 2017.
One expects reductions rankings to be based fairly, on percentages. A greater reliance on gas probably reduced emissions on the books, but not much in real terms, so easy to hide those leaks: https://cleantechnica.com/2018/02/22/emissions-fracking-5-times-higher-reported/
As your source mentions, it's probably just accounting bullshit due to the gas transition.
Of course in the bigger scheme of things, it's not good due to being insignificant. If people actually want to make progress on climate change, we need to rapidly transition away from fossil fuels, and start drawing down greenhouse gasses, not emitting them. As a wealthy country, the US should be taking the lead on that front. Let me know when the fossil fuel corporations are dead, and US hits zero net emissions, that would be something to be happy about.
https://www.bizpacreview.com/2018/11/24/fact-check-did-the-us-reduce-carbon-emissions-more-than-any-other-country-last-year-696200
One of many sources