A decent number of PA28s have their beacon and strobes on a single switch, not all of them, but quite a few. The rest are on a split switch. The SOP for those on one switch is to use nav lights instead.
Sounds like the other pilot was rather agitated and didn't want to explain.
Running strobes on the ground close to people and aircraft can disrupt people's vision quite dramatically, especially if in low vis or at night.