Used mysql command instead of mysqldump
The mysql command is an interactive shell, in which you can execute SQL-Queries (like SELECT * FROM accounts; ). Without shell redirection, it will print out a prompt (after entering the password), which indicates that you can enter a command now. This command is being read from stdin; without a quit command (or <Ctrl> + <D> to indicate EOF) this command obviously waits for input.
Without any input, the database is unaltered, and therefore no harm is being done to the database (you only killed a client to access the database, not the database server process!)