does that mean that if I purchase Accounting and Studio app subscription, I cannot use the community apps which are free.

I will be really surprised if that is the case and would like to know than the reason of stating Odoo as free. It is very obvious that if someone is opting for Odoo it will not be fore two or three apps. It will be definitely more than that as than only the whole business logic will fell in place.

Yes it means that if you purchase Accounting and Studio then those are the only Apps you can use. If you want everything free you use the Community edition. You cannot mix and match which edition you use.