The background mining system does not use a pool. It will instruct monerod to mine, and monerod does not use a pool.
Background mining has existed in monerod for a few years. It was just hard to find, and so not used much. This is the reason why it was exposed in the wallet too.
To enable background mining in monerod, you pass extra arguments to
start_mining <addr> [<threads>|auto] [do_background_mining] [ignore_battery]
Start mining for specified address. Defaults to 1 thread and no background mining. Use "auto" to autodetect optimal number of threads.
Note that since it's monerod actually mining, you can then exit monero-wallet-cli and monerod will continue mining. monerod commands work as well, so
stop_mining in monerod will then stop background mining, etc.