If I'm reading this correctly, this paper is defining excess deaths as the number of people who died in the US who wouldn't have were those people living in Europe instead of the US at that point in time? Which points to structural issues in the US system, but not to some event in 2017 that resulted in extra deaths vs. any surrounding years (just that the death rate in the US has dropped much slower than in Europe over the study timeline 2000-2017).
The US death rate didn't appreciably increase (~3 per 100k) in 2017 vs. 2016[1] and has generally been improving. That's about 10k extra deaths, not 400k, like the paper says (because the paper's usage of that term is very different than The Economist's!)
https://www.cdc.gov/nchs/data-visualization/mortality-trends...