With an ohm meter you can read DCR (DC resistance). If you have a cap in series for some you will not be able to read the DCR as the cap will not pass the DC. The 485 has a extensive crossover network so many times the basic ohm meters cannot pass the DC. So you will not get a reading. The overall average impedance of the 485 is 4 ohms.
Also, Impedance is freq dependant and a speaker is not a purely resistive load. Impedance changes with frequencies. And the overall impedance is a combination. Truly measuring the overall impedance taking into account inductive and capacitive resistance is very complex. You can measure each driver for DC resistance. But, This will still just give you DC resistance.
I think that is what they were referring to.
Let me know anything else we can do from our end