Is a sim-free iPhone different from a virtual-sim iPhone? We read that Apple has a patent on a 'virtual sim' iPhone. 

Then we saw that Apple was selling a 'sim-free' iPhone. 

Both allow you to choose your carrier later. These appear to be different concepts. 

My question is: Is a sim-free iphone different to 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