In my Dad's case, it was the former. I can't imagine my "to be" Dad being like that. If so, teacher's loss!
My dad was also a leftie who was made to be a righty. He never had good handwriting. His teacher told his mother (who was seeking advice about it) that she should have just let him be a leftie. By the time my sisters & I came along, most people that we knew were content to just let us be lefties. Two of the 3 of us are left-handed.
I'm a leftie with decent handwriting and perpetual ink and graphite smudges on the side of my hand. Fountain pen writing now is therefore a bit challenging. I was lucky. My first-grade teacher was kind and didn't force me to be right-handed. Years later, her assistant, Ruth, left, and she became ruthless. As one can imagine, the kids in her class after that were alright.
I'm told that those who were lefties in ye old fountain pen days were taught to either hold their hands above the line that they were writing and therefore already dry or to hold their hand under the line that they were writing. But as you might imagine it led to some strange hand positions which probably weren't comfortable long-term.
