- Squall is basically Rinoa's bodyguard (or... well, the knight to her sorceress, a recurring motif in FFVIII), so it's not that far-fetched.
- Gunbreaker weapons aren't meant to shoot bullets, instead they imbue the blade with various effects (consistent with FFVIII lore). That there are numerous actual GNB weapons in-game with seemingly functional barrels is... wrong, they shouldn't, yet they do.
- They do not use "Garlean" technology, not sure where you got that from? Gunbreakers supposedly predate the Garlean Empire by quite a bit, going as far back as the Allagan Empire... somehow...