In the shown screenshots, a resource pack was used to replace the furnace top texture with crimson planks, and the furnace side texture with warped planks. Note how the dispenser and dropper changed with it, despite them being completely different blocks (which doesn't make much sense as furnaces aren't a crafting ingredient for dispensers, nor the other way around).

The expected behaviour here is that dispensers and droppers would have their own dedicated textures for the top and side respectively, even if the textures themselves are identical. Note how (before 1.14) pistons had an identical back texture to the hopper top texture, despite the fact that these two textures were distinct files (demonstrated in the last two screenshots).