I am trying to find out if this is normal.
It is entirely normal to be presented with a different set of addresses when you choose a different derivation path. Some derivation paths will present you with different types of addresses altogether, and some derivation paths will present you with different sets of the same type of address.
As DireWolfM14 has said, the likelihood of you having the same seed phrase and passphrase as somebody else, and therefore accessing somebody else's wallet, is essentially impossible unless the seed phrase you are using wasn't created randomly. But if it was created by your Trezor as I think you mean, then you definitely haven't found somebody else's wallet.
I have reached out to Trezor but it was suggested by someone more experienced than myself that it might be a bug in electrum.
It doesn't sound like a bug. It sounds like you just choose the wrong derivation path on the Install Wizard. Every seed can be used to generate entirely separate legacy (P2PKH), nested segwit (P2WPKH-P2SH), and native segwit (P2WPKH) wallets and addresses. All the wallets are yours.