Then they should have been, if it was such an issue. When signing a contract with someone for millions of dollars that affects a franchise in the billions of dollars, if you are so concerned then someone on your vetting staff should be scrutinizing your Twitter feed. Let's not pretend they had to do anything but click on his name and start scrolling to find them.
As to the situation itself, I don't give a good gosh darn who "unearthed" them or why, I am just disgusted with the Disney Company for how they have handled it. I feel similarly about the Roseanne situation, so it isn't a politics issue. It's a "has the entire world gone freaking mad??" issue when some tweets this guy sent a DECADE AGO, that were publicly available all this time when supposedly he was good enough to direct two films and make a billion dollar franchise for them.
At least with Roseanne they were overreacting about something new - to fire a guy from a franchise that by most accounts he gets the lions share of credit for being responsible for the success of because someone has a fit about something he said on Twitter, freaking TEN YEARS AGO, just is saying Disney is a terrible company that you don't want to work with because they buckle immediately under any social media pressure and throw whomever the subject is under the bus without a second thought.