How am I running x86_64 programs without arch on Apple Silicon?

After getting an M1 MacBook Air, I wanted to install some command-line packages. Following this blog post , I duplicated Terminal.app and set it to run with Rosetta. Using this x86_64 terminal, I installed Nix and used it to install htop, nnn, etc. These run fine in the x86_64 terminal. However, they *also* work in the native terminal, without arch. This makes me confused, because from reading this post , I thought I needed to add arch -x86_64 before the command to run it with Rosetta. The file command tells me that the binary does not have a version for Apple Silicon. ### How did htop run successfully?