It's not just a CYA, it's a basic food safety practice. Those potato shreds were peeled & processed in a factory, where high volume is the rule. Volume increases exposure. And with frozen foods, you can't guarantee that some person along the supply chain didn't allow the stuff to defrost and then refreeze, again increasing the potential for bacterial growth (ie, letting 'em sit on a pallet in the back of Winn Dixie while someone went on break, or you drive home took 45 minutes in August with the potatoes in your trunk).
Anyway, if you actually cook the hash browns in a skillet until they're browned, you'll well exceed 165, no need for a thermometer. Insufficient temp problems tend to arise with microwaving--often microwaved items might reach a food-safe temp in one area, yet other parts of the dish aren't fully heated.