I’ll use inches since I’m American.

+/- .005 inch is a common tolerance when cutting metal with mills and lathes. Also for milling circuit boards as you mentioned. You can get +/- .001 inch if you really have to, but you’ll pay for it.

EDM and precision grinding can get you +/- .0005 on small metal parts.

Bending operations in sheet metal are more like .010 or .015 per bend. So if you have 3 bends between screw holes A and B then their relative positions might vary by +/- .045 inches.

With big parts you tend to need larger tolerances, though the parts also flex significantly. You can use the flex to your advantage by designing clever alignment features that make the part deform to fit. Plastic car body panels do this.

I hope Elon is just using a bit of hyperbole to try to motivate his engineers. If he is being sincere then he’s delusional.