I see you read 3 short paragraphs further into the article, where that was all explained in detail (except you missed the note that the farms were inherited from his father) ...
Considering that (according to this article) he later called agriculture “the study of my life”, perhaps “farmer” is an appropriate one-word summary after all.
As far as I can tell his relation to farming is limited to his obsession with the processes and geological side-effects of agriculture rather than the act of farming itself. Calling him a "farmer" would be quite a stretch, when you compare the typical archetypes of the two. Especially in the context of his contributions to natural history/sciences.
In regards to inheritance, this analogy reminds me of the two brothers who inherited a farm in East of Eden from their father. Just because you both own it doesn't make you both a "farmers". Only one brother worked the farm as a traditional farmer, even after becoming wealthy.
Also, I don’t think “farmer”, in those times had the same meaning as now. Farming was still very labor intensive, and land owners could be farmers without doing much of the work or even without being much involved in daily operations (if a large farm needs dozens of people to run it, the farms’s “CEO” won’t have much to do with digging through dirt)
Considering that (according to this article) he later called agriculture “the study of my life”, perhaps “farmer” is an appropriate one-word summary after all.