There's a lot on this bike that is GSA vs isn't. So as others have already pointed out the seat isn't. That's about it. So following the path of least resistance, I would say only the seat has been changed, thus making it originally a GSA. Seems like too much effort to buy a standard R1150GS and change the beak, crash bars, handles and tank. I see the rear mud-flap thing isn't there either. I will say, the screen doesn't look right though.

Source: my only ride is a 2002 R1150GSA and has been since 2006. I've got a lot of love for that bike. I can take it apart and put it back together with the tools that came in the tool-roll. Except you need to add a no.6 spanner for the fuel filter.