This summary is not the rule. The rule text controls.
If an employer gets more than one income withholding order for the same employee, the employer doesn't have to figure out how to satisfy every single order perfectly. Instead, the employer just needs to follow the rules of the state where the employee actually works. That state's laws decide which support order gets paid first and how the money gets divided among the different people owed child support.
This rule exists because someone might owe child support in multiple cases, sometimes in different states. Without a clear rule, employers could get stuck trying to follow conflicting instructions from different states. This rule gives employers one clear standard to follow, based on where the job is located, so they can withhold pay correctly without breaking any laws or shorting any of the families owed support.
For parents receiving child support, this means your payment depends on the priority system set by the state where the other parent works. If there isn't enough money to cover every support order in full, that state's rules determine how the available pay gets split between the different cases.