Some additional info
The power source for APU starting may be the airplane battery, a ground power source, or an engine-driven generator. The power source for engine starting may be the APU generators, engine-driven generators on the opposite side engine, or two forward 115 VAC ground power sources. The aft external power receptacles may be used for a faster start, if desired.
I'd agree the Hamilton Sundstrand APS 5000 APU for the 787 does not have an air starter like the Honeywell 331-500 Series APU for the 777 as there is no bleed system to start it, the 787 APU does have two starter/generators so does have redundancy.