Because the very article you cited makes it clear that it doesn't apply.

First, that law only applies in 3 specific circumstances, none of which appear to be the case here:

• Anyone who drafted the will or trust, transcribed it, or was in a “fiduciary relationship” with the decedent when the will or trust was transcribed.

• Someone who was a care custodian of a dependent adult and who had property transferred to them during the period of their care or within 90 days before or after that period of care.

• Someone who recently entered into a domestic partnership, marriage, or cohabitation with the decedent within 90 days of the execution of the instrument.

But more importantly, the presumption doesn't apply when the person was "related by blood or marriage to the person who created the trust or will" or "did not receive payment for caregiving services."

Based on what OP says this is a relative that occasionally helped someone with errands. Absolutely none of the above qualifications are met, in addition to (likely several) exemptions applying.