There are a lot of assumptions made in the article, not the least of which at the individual caught that particular type of malaria locally. They made their money through trade, correct? Wouldn’t that apply some sort of travel? I suppose it is possible they caught the disease while hunting on there hunting grounds, but there is no evidence of that.
Sorry about the typos. I am trying to do this voice to text.
The Medici family began with a different business, run as was usually the case throughout the world prior to WWII, out the home. So successful were they, they started lending money to others needing what we now call seed money, but did their due diligence. They were not the first to do so in Florence, and private lending rather than what we have in modern banking systems was also the rule during the Roman Empire.
The Medici bank wound up opening offices in cities throughout Europe, and may not have been the first international lender, but definitely helped transform lending into an acceptable form we recognize today. Sometimes the Medici family did travel, but I suspect that was more of a last resort thing in the case of their businesses.
So, they could have been exposed to malaria anywhere, technically. The Arno valley though is still a good place to be carved up and carried away in pieces by mosquitoes, so there's probably not a good reason to doubt this new suggestion.