tmpfs : creating file in tmpfs does not change memory usage in htop/top

I read about tmpfs and got curious to get the benefits from it. So, I created a directory and mounted as tmpfs.

So, as per theory, whatever is written in tmpfs gets stored on RAM directly and lasts till reboot. So, I created a 10 GB of file on tmpfs drive. As per theory, htop/top command must show RAM consumption to be more than 10 GB. I have 256 GB of RAM, but my RAM consumption was less and same as it was before creation of 10 GB of file on tmpfs.

Is there something that I missed out?