A voter has to have an identified designee to drop a ballot. In most counties, if you look at your voting guide, the designee is listed as a family member. The whole point is to prevent ballot tampering and fraud—someone filling out your ballot and turning it in in your place. A county may try and reach out to the voter if there is an issue, but there is no guarantee.
If you look at the back of your ballot envelope, there’s a section for a voter to identify the designee and sign. It includes a name, relationship, and a signature line.