That's manufacturing based in dollars which is quite misleading. Rolling with your example of planes, this [1] is how a 737 looks in terms of manufacturing. Boeing does a lot of assembling, but the majority of the manufacturing is outsourced.

When people think of manufacturing they generally think of going from basic materials to something useful, rather than 'just' assembling quite advanced parts. Like if I go buy some parts and 'build' a PC that'd technically be manufacturing, and quite high value manufacturing if I was able to sell it at a good markup.

[1] - https://www.visualcapitalist.com/cp/boeing-737-global-supply...