Proper USB power supplies have the USB data pins shorted out, or a special resistor divider configuration to signal power delivey capabilities for Apple devices. No actual USB data communication. I would be very curious what is going on, are you willing to take apart the power supply?
Maybe a smart-ish charger that can identify Samsung or other tablet for fast charging and iPad see the foreign crosstalk as a potential controller.
Also could be a way to encourage sales of apple authorized chargers...
There could be something shady going on but I've seen this message occasionally with my OEM cable. Realistically, what could a secret device in your cable do?
Can you take it apart? Even if it was spying, how could it connect to Wi-Fi. Also how could the OEM connect to it?
Did you buy it from Amazon by any chance?
It's a warning that it's not an Apple-approved device
It may (or may not) be "shady"
It's an especially helpful message when plugging into a not-before-seen computer
It's also helpful as a warning that you may not have as high a QC standard for the charging device as you should for your $1000 pocket supercomputer we call a smartphone