That just applies to visitors on visit visas.

One week on local license, then temporary driving license.
An International Driving License is valid for 6 months from the date of arrival in Qatar.

That's why visitors can stay for a maximum of 6 months before leaving or getting a RP.

Once you have a residence permit you are bound by law to get a Qatari driving license. Anything else is illegal. Let's make that clear.