If Tesla (EM) did not sell all that BTC, then it would be more accurate to say that it is an unrealized profit - and EM has stated that it has no intention of selling that BTC, although this may change at any time. In addition, Tesla appears to have bought a total of 46 000 BTC at an average price of $32 610, but sold 10%, so the total amount of BTC is now 41 400 currently worth 2.375 billion.
This was my first thought too, but journalists like to count someone's unrealized gains and losses, titles like "billionaires made trillions in last year" actually mean the same thing as in this article. And I think in this case it's a positive thing, because people who will hear that Elon Musk made a billion from Bitcoin could get interested and eventually buy their first coins too.