It has to do with how the energy of the candle is moving, rather than how much energy the candle is generating.
Basically, the clay pot is trapping the heat in a lower portion of the room, and allowing it to radiate and convect and conduct in a portion of the room that people actually occupy, as opposed to convecting it up to the ceiling where no one is.
Remember, what people call "science" is the body of knowledge gained using the scientific method. The model we currently have of the universe is pretty good, but it only can tell us what happened a few fractions of a second after what we call the "Big Bang" occurred. We have no idea what happened at the moment of the BB, nor can we even hazard a guess at what happened "before," if "before" even makes sense.
Think of a yardstick being the universe running from beginning to end of time. What happened to the universe "before" the start of the yardstick makes no sense, as you are saying "what's on the yardstick before the yardstick starts."
The class of virus is corona virus. It denotes the general physical shape of the virus.