That's the tolerance on paper, but the dude was doubting that you actually achieve that tolerance in the field. How can you when (using your supersonic aircraft example) you need to deal with temperature fluctuations more than 100c, not to mention pressure changes and sheer forces, which all deform the part?

Were they temperature controlled deep in the craft? On the leading edge, things can get up to foundry temperatures and so thermal expansion can reach the percents.

I guess you could design something to self-compensate for that, like the old gridiron pendulums, but that's a big ask on top of a task that already sounds daunting.