I am not certain but it is possible that this was a secondary market purchase. The fact that it was announced by the Prince and not announced as a funding round by Twitter suggests a secondary market purchase.
In other words, the Saudi Prince may have bought the stake from an existing Twitter investor.
That is a good find but it is not dispositive. For various legal reasons many people want secondary market transactions in securities that are not registered to happen through the company. So this may still be a secondary market transaction, but I am sure we will find out soon enough.
In other words, the Saudi Prince may have bought the stake from an existing Twitter investor.