This a Real Cloud not a puff of smoke, just like the ones in the sky, made of microscopic water droplets but trapped in a closed building. It’s completely artificial unlike naturally-generated clouds.
Architect of the read clouds, Testuo Kondo thought that putting them inside the building could be a good idea. Since he couldn’t herd a Cumulonimbus through a window, he asked climate engineering company Transsolar to actually create the cloud itself. To do that, the company pumped three layers of air at different humidity and temperature points, and then used machines to generate the cloud itself, which floated still in the middle of the empty space.
The resulting combination made the cloud stay in its position, just a about meter above the head of the of visitors.