A billion of UNREALIZED PROFITS.
At least Cointelegraph specified that these are unrealized profits that Tesla got since they aren't selling their Bitcoins at this moment and right now, they have no intentions of selling it.
I'm thinking if what will be the effect if Tesla said to the public that "It is a hard decision but we will sell the Bitcoins that we are holding for the betterment of the company"

. Not exactly the same but you get the point. Maybe it will have a huge effect into the investors themselves and possible negative. It might also create a more selling pressure thus, causing the price of Bitcoin to go even lower. This might not happen though and the opposite might happen as well. We don't know but I'm curious with it.