Because agents is different than conventional software:
1. They behave differently: non-deterministic vs deterministic
2. They have different mechanism: harness+llms vs codes+apis
3. They have different interfaces: clicking vs chatting
They are like boston dynamics robots vs humans
Pi is just the harness. I think in case of the article that is what they mean when they say agent.
You can write one in 200 lines of code. Just a TUI for an api.