no paint or lining, I've had many concrete tanks before when I still live in Vietnam. We just let it cure completely then fill it up with water, let it soak for a few days then drain and fill the water back up. Do that repeatedly for 2-3 times and the tanks are safe to put fish in.
I've had good luck with pond shield by pond armor.... Hard to say from the video but you can get away with no liner u just get more evaporation/wicking away. Vinegar canhelp stabilize an unsealed pond in first few fill/rinses as well. Where I work we seal ponds like pools with plaster