Yes the frozen hash browns you buy in the store are precooked and usually just need thawing out and then heated up in a skillet or oven.
The shredded potatoes are usually blanched in oil or sometimes water and then flash frozen.
The frozen hash browns are made to be ready to heat up and eat without doing much cooking.
All I need to do when buying frozen hash browns is to put them in the oven for around 10 minutes and then they are ready to eat.
You can also heat the hash browns up in a skillet with some cooking oil and then flip them over every few minutes and it usually takes 5 minutes to 7 minutes to heat the frozen hash browns on the stove in the skillet.
Mostly I prefer to heat the frozen hash browns in the oven but sometimes I'll use the stove and they turn out pretty good either way.
Potatoes are very safe to eat raw so even if the frozen hash browns you bought were raw and you just heated them up a little then nothing bad will happen to you.
But the hash browns are almost always precooked.