OS X reinstall remembered my wi-fi password

I'm having the same issue with the wifi password persisting... I took different steps than Captainlonate. https://discussions.apple.com/thread/6256023

Using two computers... I downloaded catalina from computer A and installed it to a USB stick. I used that USB stick on computer B to boot up from, delete the contents of the hard drive, create a new partition to install on, and then install catalina. At no point during the restore process on computer B did I put in the wifi password or iTunes password.

Computer B was on the wifi network prior to being erased.

So... My question is... how do you safely wipe a computer without any information being passed? Was the wifi password saved in the Image that I downloaded and installed? Or is erasing the hard drive not really erasing it?

Thanks!