Because they don't have the same zero point. 16 deg Celsius on the thermometer is 60.8 deg Fahrenheit, but if you're measuring difference, you have to do 16 - 0 C = 60.8 - 32 F = 28.8 F. Or to make it clear, 16 going to 32 C is 60.8 F going to 89.6 F, also a difference of 28.8 F.

Or just do 16/5*9 without adding 32, so you'd get 28.8 F.