That will be down to the translation and how suffixes like "-san" and "-kun" were handled. Occasionally you do get things like "Barret-san" rather than "Wallace-san", and obviously the closest thing to that is "Mister Barret".

I'm fairly sure "Professor" as a title isn't a suffix in Japanese, so the usage couldn't be the same as "-san", but I can't speak to that, not being an expert or having studied it at all.

VII's localisation was pretty terrible.