Could someone explain what is meant by a non-one-time-use externally owned account and what is used (or misused) for?
EOAs are user addresses i.e. not contracts. A "non one time use EOA" would be an address possessed by a user which is used multiple times rather than used and then discarded - such as MetaMask accounts. This is bad practice in terms of privacy, but good for tying a specific user to an address. Wherever you read that was probably referring to one or the other, I'd guess.