A hundred years ago animals bred for food were not managed in the same way as today. Animal husbandry was very different.
I am vegetarian for two reasons and religion doesn't enter into it. The first reason is I don't like the idea I would be eating an animal, the second is how that animal lived and died. Being really honest, I am not sure if I would have become vegetarian if I thought animals bred for food were treated well and I didn't have concerns about animals welfare.
If I was the homeless man and very hungry, I would have accepted the gift and thanked the person for their kindness. I would have scraped the tuna off the bread and eaten the bread. We're lucky that we live in a country where there's places where he could get food, so he was not starving. I would guess if he was starving, he would have eaten the entire gift.
So yes, attitudes towards food have changed, but so have attitudes towards animal husbandry. Unlike a hundred years ago, most people these days have no idea about the processes used to fill our supermarkets with meat, poultry and fish. They don't want to know either.