An amateur historian has discovered a long-lost short story by Bram Stoker

It's funny (ironic?), but when I read "an amateur {insert occupation} has"

I mentally replace "an amateur" with "a talented and passionate"

For me, amateur just doesn't mean the insult that it meant when I was a youngster.

The word 'amateur' originates from the Latin word for 'lover'.

Exactly, and "professional" means they do it for money.

The point is that "amateur" means literally "lover" in latin. While "professional" means "for money" today, in latin it meant "to profess a vow to do it with high standards".

For example, you can be a professional, but do things "pro bono" (for free or for public good) or "pro lucro" (for money).