It's the first time we've had the biotech to follow the evolution of a viral pandemic in real time. We already mostly knew how it transmitted. Most of the discussion was really around the edges. We knew coronaviruses transmit mostly by air. But there was a really technical quibble about how far the particles that carry the virus could spread. Some viruses spread with very small particles in the air and can stay in the air for a long time. For others the particles that carry enough virus to get you sick are too large to stay in the air. They mostly settle out fairly quickly. The sanitizing groceries thing, it's still possible the virus might transmit that way a very little bit. It's not enough to be important however.

The hard part about studying transmission is that you can't do the most direct experiments that would settle the question. It's considered very unethical to intentionally infect someone, even infecting healthy informed volunteers is pretty controversial. Which is what would be need to answer the question directly. So you have to watch for "natural experiments" where things just happened in a way that you can get the information. You have to be pretty lucky to find them unfortunately.