I actually thought I'd read on here about the apu starter motor brushes in a previous thread/search
That would be correct. APU starter motors are much more like a car's starter motor, in that they are electric motors and are powered by the aircraft's battery. Once started, it's the APU that supplies bleed air to the main engine air starters.
So yes, you read correctly. However, that only applies to APUs.
Cheers,
John