He's referring to Ledger hacks and leaks, due mainly to having so many different chains available on their device... And Trezor moving that direction.
Discussion
I think nostr:npub1a953zfv04wmuyd0lhvzje94q00u370hernaqxmj0gshayveqyc0sj4gpn5 meant “[they] don’t understand” that Bitcoin-only is the way. 😎