If he is probing the solenoid's + terminal and ground, the starter and the voltmeter are in parallel, so if there is high series resistance through the wiring or the maze of relays, then a high voltage does indicate that electric power is being delivered to the starter.I missed where you said "electrical getting to the solenoid", but that should be explained. For example, if you hooked a DVM between the solenoid terminal and ground, you might easily read battery voltage when the key is turned, appearing to mean the circuit is OK. But there could be a dirty or burned contact in the circuit causing thousands of Ohms resistance, and while there would not be enough current for the solenoid to work, the meter (because of its extremely high resistance) would show battery voltage or very close to that. This is why the recommendation to use a light bulb (and not a Voltmeter) to check the circuit.
If there is any question of power reaching the starter, one can always bypass/jumper the PRND/clutch relay and the security relay to test if one of these is at fault, but if you are bypassing PRND/clutch you have to promise to attempt to crank only in P or N, since you will have bypassed what the DOT has long considered to be an essential safety feature.