Well, for those that are buying a new iPhone 6S or iPhone 6S Plus at a store (any store, not just Apple Store), I don't think they would allow installing software during the "testing if the device is defective" phase, nor would they allow plugging them into a Mac and running software to test the device.
If the iPhone 6S was on display, or was second hand, I think the video would allow you to see the model just by looking into the logs as shown in the video. Because at one time or another it must have been drained fully on its own. However, the problem is with a new phone out of the package. It would be difficult to force a battery drain unless the phone was not fully charged before packaging. I am not sure, but I think some phones are not fully charged out of the box, and in that case, it might still have the low battery logs.
If the iPhone 6S was on display, or was second hand, I think the video would allow you to see the model just by looking into the logs as shown in the video. Because at one time or another it must have been drained fully on its own. However, the problem is with a new phone out of the package. It would be difficult to force a battery drain unless the phone was not fully charged before packaging. I am not sure, but I think some phones are not fully charged out of the box, and in that case, it might still have the low battery logs.