This is not only a fun April Fools joke on the surface (Tesla introduces a Watch), but it is a much better joke when you dig down a little deeper and see that Tesla and Elon are making fun of the stock market's short attention span.
Elon doesn't want to take SpaceX public because of this very fact, the market doesn't know how to have a 20 year vision of putting people on Mars let alone the ability to read under the headline.
The fact that the press release was made only 5 minutes before trading closed might, in fact, support this idea that it was aimed at automated trading as a human wouldn't have had much time to react to the news so close to the end of the day.
On the contrary: if humans take more than 5 minutes to react, then releasing a joke 5 minutes before trading ends has no risk of harming the stock if people misinterpret the press release as fact.
Elon doesn't want to take SpaceX public because of this very fact, the market doesn't know how to have a 20 year vision of putting people on Mars let alone the ability to read under the headline.
All great jokes are rooted firmly in reality.