What are the metal shavings in my bottom bracket from?
Some possibilities:


The seat tube or theoretically the head tube was reamed after the bottom bracket was installed, either at the factory or during assembly or service.
A little deposit of cuttings somehow got lodged in the seat tube or down tube from any of the many manufacturing steps that could create them, perhaps sticking to the inside of the tube with the help of some cutting fluid, and they made it all the way through the process but came loose over time once the bike started being ridden.
Some kind of simple brain fart, or laziness, or apathy, or some combination thereof on the part of whoever reamed the shell or seattube or assemeble the BB/cranks at the factory.
One corner case scenario that's theoretically possible with all cartridge bearing bike components is the bearing seizes due to extreme wear, alignment, fit, and/or quality issues (maybe some other factors too) and the spindle, axle, or bearing bore they're supposed to have stationary contact with is now a dynamic contact, which will start wearing away material, in this case from the crank spindle. If something like that did happen here I'd have no idea how the material got lost in such a shaving-like way, but I've seen weirder


It's not necessarily connected to the creak in any way. BB30 is simply prone to creaks.