Social network icons resolution and sizing

Earlier in the video, Nick states that we should resize the social media icons while maintaining detail for high-res displays.

He used pixel sizing specifically when making them smaller (20px, approximately half of the original size).

However, what if I used percentages? such as 5%, would the detail remain, or be somehow lost? I tried it at 50% just for giggles, and those things became huge, and also lost some of that sharpness compared to the smaller, original size. I also tried it in pixel measurements at 100px height and width. Same thing (although quite smaller than 50% size).

Now, personally, I don't think it matters either way (pixel measurements just makes things a little easier to predict). I do a lot of photography, and I know that the less pixels you have in an original image, the less detail it holds overall which you can see more easily as you enlarge the image past its maximum. A smaller image just makes things... smaller. Harder to see fine detail, but makes the file smaller as well.

Perhaps I'm missing something here though. Granted, I know I'm WAY overthinking this, but I'm simply curious.