I think you're on the right track about more people getting tested.
Stats are a day or two old, but I think it shows the trend.
US fatality rate continues to fall -
4.06% March 8 (22 deaths of 541 cases)
3.01% March 10 (30 of 994)
2.52% March 12 (42 of 1,695)
1.93% March 14 (57 of 2,954)...