Probably just casual rounding of a quantity and its reciprocal, without realizing that 4% vs 5% is a large difference.

Maybe it's actually 4.48%, which would be about 1 in 22, and they rounded in opposite directions.

Indeed, 4.5% would be 5% when rounded in decimal, but it's 1 in 22.222 in fractional, so 1 in 20 and 5% both are valid choices with normal rounding.

For a company of 70,000 people, 4% leaving is 2,800 people and 5% would be 3,500.