The same thing happened to me, I took a video of it but can't display it here somehow.
My iPad mini was at 5% and I was not none with it, so I connected it to charge and kept using it.
Shortly after my arm started getting a warm feeling, then I see some smoke. I looked around, the actual genuine Apple lightning connector is on fire. The whole cable is hot and even on the USB end the white plastic is melting.
Note that: Cable was in excellent shape, looking like new. Except for a minor dark discoloration on the center of the connector itself. It was the only cable able to charge my iPad. I bought certified cable on amazon "the iBlazon" and other genuine Apple white one none would work.
Granted its rare something like that can happen but the lighting connector, can potentially burn your house down if your not there. Maybe some house fire and death already have occurred because of unattended iPad getting Charged up. I will share my experience with my local Fire department, I feel obligated because live are at stake.