Yeah I think you are right, I should say that some of that code was ported and still survives today in 26 uses some of the same APIs and naming, but isn’t necessarily the same code from classic Mac OS. One example is RegisterEventHotKey.
RegisterEventHotKey() is available "in CarbonLib 1.3 and later" according to Universal Interfaces.
This was never provided by classic Mac OS and many apps hacked it in by hooking Get/WaitNextEvent. In Carbon they didn't support this sort of "mangle the global system callbacks" shenanigans, but there was a real developer expectation of this API, and Apple was begging developers to port to Carbon. This API filled that gap.