Why do folks interested in plants refer to themselves as "botanists"?

[AdamWargon]

From another thread:

@wdvanhem

Bill Stewart (1923-1997) was one of the most prolific botanists in southwestern Ontario in the second half of the 20th Century. He was co-author of the Guide to the Flora of Elgin County and published dozens of botany articles in his lifetime, including several peer-reviewed articles. He collected thousands of specimens which have been deposited in herbaria around Canada and the United States.

You might be inclined to call Bill an expert botanist, but he had no formal training in botany and his most advanced education was a diploma from a trade school in a small Canadian city. He was a tank operator in World War II and later a tool and die maker before landing a job as a technician at a local university.