Security question about a GETH testnet node.

Asking this for a friend (truly)- He had a GETH node running on sepolia testnet and opened his firewall port 8545 while testing something out without thinking it through carefully. He started getting a bunch of “served eth_sendTransaction” messages in terminal that were accompanied by “err=unknown account.”

He shut down the node and we are both fairly confident that someone calling remotely into his node wouldn’t have the ability to breach his computer or network more deeply. Is there reason for concern?

Thanks!!