Under the hood, Electrum derives a "master private key" (m) from the seed and derive external and internal chains at (m/0 and m/1) for receiving and change address parent extended keys.
Then, the addresses which at (m/0/0~19 and m/1/0~9) for the initial 20 receiving and 10 change addresses.
This is only the case for legacy wallets. Electrum uses m/0' (rather than just m) for single-sig segwit wallets, which has obviously been the default wallet type for some time.