I assume its mostly rounding errors with small numbers, especially with the 'Used" only giving one decimal point, while the "added" two. and assume these are numbers pulled from the API. I don't think Teslafi does any calculating, but just shows the info the car records.
here's a couple other examples where the math works out closer
Used 11.5kWh, Added 11.52kWh, Charging Efficiency 100.5% (figure that one out)
Used 73.9kWh, Added 68.91kWh, Charging Efficiency 93.2%
Used 31.8kWh, Added 30.38kWh, Charging Efficiency 95.4%
Used 39.3kWh, Added 34.98kWh, Charging Efficiency 88.9%
Used 21.2kWh, Added 20.10kWh, Charging Efficiency 95%