In any case, this toy detail was intended to snuff out the grandparent's presumption that 10x error in any arbitrary parameter is obvious. The difference between 6061 and 7075 is offered as a simple thought experiment in that they're both common alloys in industry, yet difficult to discern one from the other despite the latter having a zinc composition that's 20x greater in the best case (6061 = 0.25% max; 7075 = 5.1-6.1%; 20 ~= 5.1 / 0.25) as specified by ASTM B209[2].

Fact of the matter is a contractor was responsible for a build-to-print submarine. A particular drawing specified something-or-other with an off decimal value that escaped human detection during multiple engineering design reviews. Contractor had something-or-other manufactured to the exacting detail specs in said drawing and no doubt was able to provide supporting documentation in the form of material certificates of conformance and lot testing results...but all the precision instrumentation and manufacturing quality control in the world amounts to nothing if the basis of truth is fundamentally flawed...and it certainly didn't help that the only effective opportunity to detect catastrophic design error (not that it's a build-to-print contractor's responsibility to identify such subtle faults) was spot validation of a system-level key performance parameter that wouldn't have been possible until the entire system was fully assembled.

[1] https://www.nist.gov/system/files/documents/2019/12/03/00-20...

[2] https://www.astm.org/Standards/B209.htm