A nurseryman was someone whose business was raising plants. A nursery besides being children's quarters is a rearing place for plants. Nurseries pre-dated garden centres. Some still exist. Flower shows are a good place to meet nursery(wo)men.
Nurseries vary in size. Smaller operate from owner's garden/ farm /land, selling plants on-site, or at a street / market stall, flower shows or by mail order. Larger may be size of a garden centre. Emphasis is on plants & related material . Plants may be grown from seeds, cuttings etc. on-site, or bought as very young plants and grown on.
As to how successful your man was, you'd have to do more research on him.