This is an element of how rasterization is performed and has no implication on if graphics are 3D or not though. PS1 hardware having no perspective correct texture mapping doesn't make the games that used it "not 3D" - and on the flip side, a side scrolling 2D platformer using a rasterizer capable of perspective correct texture mapping (like any platformer that uses OpenGL or Direct3D to render its worlds as triangles) doesn't make the game use 3D graphics.