TL;DR: They include debits and credits from historical transactions in the blockchain, not just unconfirmed mempool transactions.
The “Total Received” includes not only the amount received in unconfirmed transactions in the mempool but also historical amounts previously received in past transactions that are already confirmed and therefore no longer in the mempool but in the blockchain.
The “Total Sent” also includes amounts in confirmed transactions that spent (consumed as inputs) amounts that had been associated with this address.
The balance is the difference between the two. All amounts ever received at that address minus all amounts ever spent from that address.
