But... I don't remember it like that in SA on the PC at least. Weird. And I'm very sure III even had an option in the graphics settings to enable widescreen support, which was pretty odd. Why not just assume square pixels and figure it out from there...
I don't think it adapted at all to 16:9. It is just stretched.
Even PS2 games that had the option for widescreen sometimes left out things like menus and the HUD. It was pretty hacky, but I played PS2 on a 4:3 screen for years before I had anything else. Never seemed like a big deal.
I'm kind of annoyed they didn't standardise options for it on that console. Some games set it in the menu, others had a (bespoke) button combo you had to hold down while you started the game. Having a PAL system, it was interesting how hit or miss switching to 60hz mode was on various TVs, when EA racing games would prompt me about it.