I think that it is a little different than that. It is just like the recent True Grit movie. That was not a remake of the 1969 version starring John Wayne. No the more recent movie was an adaptation of the source material...a novel.
So this Starship Troopers will not be a remake of the other movie but an adaptation of the source material...a novel.
The Amazing Spider-Man reboot isn't a remake of the previous Spider-Man movies either, but a new adaptation of the source material... comic books.
The recent True Grit was commonly referred to as a reboot as well. All that really means is a fresh take on an established property. Again, I'll say it's purely semantics.
I'm sure a distinction is being made on how closely the films are based on the source material, but unless I am mistaken, we really don't have any information on what is being planned for the new Starship Troopers movie.
Edit: Thinking more -- I'd argue 'reboot' is defintely the right word, because the previous Starship Troopers was a film franchise with a couple of sequels (albeit direct to video) and I'm thinking maybe even a cartoon (no?). By ignoring that continuity, Sony is definitely rebooting Starship Troopers as a film franchise, and you can be sure they will pursue sequels, etc. if this proves to be successful.