I'm guessing you didn't play past the first area, because it's only once you're in the wilderness when you have to do a lot of backtracking to use new firearms to open up previously inaccessible areas.
I have completed this game. There is no element of non linearity whatsoever. That's like saying pokemon is a metroidvania
Buddy it just sounds like you don't know what a Metroidvania is. MetroidVanias don't have to be nonlinear or open world
Despite the openness of the game, progression is usually linear, with the more difficult areas separated by natural barriers such as high shelves, sealed or locked doors, or other obstacles that can only be bypassed by finding specific items or weapons. Among gamers, Sequence Breaking is a common stunt used to access these areas before the player is "supposed" to.