I'm trying to purchase hub-centric spacers and I see everywhere I look that it would be 67.1mm. However, that isn't the case with my car as its imported.
Am I an idiot?

 

I wouldn't worry about it since that's not a dimension that should have ever changed throughout the FD's life, but if you're insistent on confirming it by measuring, ask yourself this. Are you certain your caliper is properly calibrated? Are you sure you're measuring at the correct location? Are you sure there isn't something throwing off your measurement? My recommendation is to remove the brake rotor and use a tape measure to check the circumference of that cylinder you're trying to verify, then do a little math to come up with the diameter. My experience has taught me to avoid using calipers the way you have shown in your picture. I would prefer a micrometer, but that's not exactly something that everyone has lying around. The caliper could probably give you a better reading if you could orient it parallel with the brake rotor, but that's not an option thanks to the wheel studs.

 

Are you sure you don't have an aluminum hub ring already on there? It looks like there's a ring around the hub already, although it may just be my eyes.

 

Yea looks like there is a hub centric ring already on there and at 73.1 thats a common size for aftermarket wheels.