Is a sim-free iPhone different from a virtual-sim iPhone?
No no, Apple is selling the phone only, without a SIM or a carrier plan.  That's what SIM free means. The device ships without a SIM. You need to buy a SIM card separately . But a virtual SIM is a completely different thing.
A virtual SIM is a concept in which no SIM card is needed and the protected storage is inside the phone. So you can switch carriers without changing a SIM