That is the same setup as Lexus. Lexus climate control is setup the same way.
The reason A/C turns on is that is the best, quickest way to get the temperature to the desired setting.
Also realize that regular use of your A/C helps it last longer. If you don't use your A/C the seals and system are more likely to dry out, crack and begin leaking. Read your manual but I think most suggest using the A/C at least once a month.
Remember A/C can be used for HOT or COLD air. Some people think A/C is only for cold air but it isn't.