I made up my own wallet address and mew logged me in !!

1. I created a tether address with a mnemonic on another wallet –

2. copied address and edited it in notepad, changing a few letters here and there.

3. Put the address into myetherwallet.com mew and it logged me in.

is that how eth network works? we can make up an address and as long as it is the right length of character and mew accepts as a private key the address can be used to receive tokens from the base network selected ?