I think that there are many factors. Here are just a few that I can think of:
- The room's acoustics
- The room's size
- The microphone
- The distance between the keyboard and the microphone
- The angle between the keyboard and the microphone
- The combination of both the distance and the angle
- The surface the keyboard is on
- The way the person is typing. If someone doesn't bottom out at all with Cherry MX Browns, then their typing will sound extremely different from someone who bottoms out while typing.
- I suppose the software they used to edit the video comes into play too. I'm considering how even some 360p videos have a way better sound quality than others.
- Whether or not the 'feet' on the keyboard are being used
I can't think of anything else, but all of these things lead to one fact: in order to get the best idea of what the actual sound of the keyboard might be, listen to as many different recordings of that keyboard as you possibly can. After a while, you will start to recognize that there are certain characteristics of the sounds that are always the same from video to video. Before long, you'll start to have a fairly good general idea of what the actual sound might be in your room.