I think it started out in ROM, it has low core jump vectors so that portions can be replaced (rather than just the whole thing) I worked designing Mac graphics accelerators back in the day, we hooked them up by replacing bits of QD through these vectors. So over time rom fixes got made and some of it would have come off of disk
If you follow that second link you'll find a zip file with quickdraw source in it, you'll find that while there is a little pascal (.p files) most of the core is assembler (.a files)
Good point. The Amiga did the same thing in the Amiga 500 and 2000. The Amiga 1000 would have if the operating system had been more stable at time of release. It also saved a significant chunk of RAM as the 1.x releases of AmigaOS used 256KB ROMs while 2.x on were 512KB ROMs.
If you follow that second link you'll find a zip file with quickdraw source in it, you'll find that while there is a little pascal (.p files) most of the core is assembler (.a files)