This happened to my friend that he created an account on forum and when he got in, there is a red note on top of his page means banned and needed to pay some btc. I just told him to create account not using their wifi and create somewhere else then boom he got an account that isnt ban.
This example doesn't show that the evil points decayed, as it happens very slowly and your friend would be waiting a long time to be able to freely open an account. As you said he switched from using a public WiFi to a more personal connection, which means changing IP address, so he simply moved from an IP with evil points to one without.
Note that evil points associated with a particular IP reduces with time, but when an account is already created from that region and associated with some units of evil, the user needs to pay to enable posting as the evil points linked to an account does not decay with time.