Ledger Nano is a hardware wallet, but it is not the only hardware wallet. Even if you want o use hardware wallet as an example, is it ledger nano that is not absolutely open source that you should recommend when open source hardware wallets are existing.
That particular thread that you are talking about is a personal review written by OP based on his own impressions and experiences with the Ledger Nano S. That's the hardware device he owns. He didn't simply pick one randomly to review and write about. If he purchased a Trezor back in 2017 when he bought his Ledger, his experiences and feedback would be different because it's a different device.