Agreed. This sort of issue has been public knowledge about Twitter for a long time. This sounds to me like an excuse to delay or get out with plausible deniability.
So it may be a question of just how dishonest Twitter has been, which could/should result in shareholders suing them as well.
But he did know it was a problem [1], so it's at least a bit shifty that now he pretends he suddenly says that it is a deal breaker. I suppose a court would have to decide if he has a right to back out or not without repercussions.