I think Trezor can be used as a cold storage since it is possible to sign a transaction offline with it and broadcast separately to the bitcoin network. You can go ahead and create an unsigned transaction with electrum wallet, the unsigned transaction would be saved a PSBT (Partially Signed Bitcoin Transaction). Then you can go ahead connect Trezor to a computer and use the wallet software to sign the transaction without the internet.
After that you can send it to the network using online broadcasters like Electrum, mempool.space, e.t.c
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What you wrote is true, but you can achieve the same thing with an even better level of security if you install Electrum on a computer that is offline, and then create a watch-only wallet on a computer that is online. That would be a cold + air-gapped wallet by definition, while with Trezor you still have to connect it online when you install firmware and coin apps (unless there is a way to do it via SD card).
Simply put, anything that has direct contact with the internet is not a cold wallet.