Again, I don't want to take anything away from a lightly-modified production car running a sub-1:30 lap at Willow with street tires on it. That's awesome, and it's a real tribute to both Rif's driving and BMW's design and engineering.
But when I Google the question, I find actual BMW owners getting weights in the 3,350-3,450 range, which makes sense if you take the official figure (which I now see is 3,649, thanks to bawareca), and subtract the EU-mandated 165 pounds for the driver, and then subtract the weight of a full tank of gas (which owners like to exclude when they're trying to get a low number like 3,350). It makes sense then that I keep seeing the 3483 figure, since it's 3649 minus 165 pounds.
3,649 EU curb weight drops to 3,483 US curb weight. And that EU weight includes 16.6 gallons of gas, which weighs about 100 pounds -- which would bring that figure down as low as 3,383 when you roll onto the race scales. At that point, individual scale variations and pulling the tool kit or whatever would get you into the ballpark. Options like a sunroof, leather, wheels, exhaust and such will skew things too.
All of which doesn't matter, really, when you're looking at Rif's lap time -- which is impressive.