2) I'm disconnecting the ethernet cable from the computer after downloading Electrum.
3) No one can see the screen.
1. Are you sure? If it were a CD, then you know nothing can write to it. USB is usually not write protected.
2. Did you check if the wifi is turned off or bluetooth, or any other peripheral device or add-on is there? Did you check the keyboard is not a keylogger?
3. How many other people are in the room? Can you see the CCTV camera behind you that's as small as a phone camera?
Just don't do it in a public computer if at all possible unless you have no choice. If you're creating cold storage, we can assume it is for a significant amount. If it is for a life-changing amount in value, then it's worth more than the price of your own hardware. Get your own laptop or computer or tablet.