Say I have an Electrum HD wallet and give my Master Public Key to an external service (like CoinSimple for example: https://coinsimple.com/support/how-can-i-accept-bitcoin-directly-to-my-electrum-wallet-using-coinsimple/ )

That service can use my MPK to derive addresses that receive money in transactions.

How does the Electrum wallet know about those transactions? 
Does the wallet make RPC function calls internally to search/import for these transactions and addresses?