Does a proprietor is bounded to conduct only export sale not domestic sale if he has IEC, GSTIN

One of my friend running an audit company told me that If I register and took a IEC for export and get a Current bank account and GSTIN then I am bounded for only export sales and I can't make domestic sales transactions on that same GSTIN ?

Logically I felt this is not possible but I am asking if is there any rule on this that if I am planning to run a proprietorship and get GSTIN + IEC + current bank account to conduct export then I am not allowed to do a few domestic sales transactions?