No, it doesn't depend on how they got the rating.
They get the rating by meeting the standards of the rating. There is no other criteria. There are no alternate methods.
The iPhone 7 is IP67 rated, which means it's can go to 1 meter for 30 minutes. Samsung has an IP68 rating, which goes to 1.5 meters for 30 minutes.
It's important to note that neither rating is for any kind of additional pressure, steam, or chemicals. So showers are not a good idea, neither is holding it under a faucet. Chlorine from pool water is also not great.
I would not take the results of one video as conclusive at all or proof of anything.