Why would one person use the term "robber baron" and another "captaion of industry" to describe the same person

This would all depend on the person's life experiences and perspective.

For someone who works day in and out on a factory line receiving little pay, the person who owns the factory is likely to be a robber baron as they feel like the person is profiting off their hard work.

To someone who also owns factories, their fellow owner of industry is likely to be a fellow captain of industry.