Well, that's not what he said, and he still is one of the world's best mathematicians. So one wonders why you would take that surprise as indicative of a mistake on his part rather than on yours?
Well, in science there’s a simple rule: your substantiate your claims.
A plausibility argument like Tao’s one is simply not an argument.
To show that Mochizuchi is wrong you need to point out which equation of his work is wrong, which by the way is Peter Scholze’s plan.
Tao by his own admission does not have the background to evaluate Mochizuchi’s theory and still gives this worthless plausibility argument, appealing to his knowledge of other unrelated proofs. I’m astonished.
Except that he doesn't say it is incorrect, he says that "it seems bizarre" to him that seemingly Michozuki's paper doesn't have any uses beyond proving the ABC conjuncture. The rest of this comment is just explaining how it's usually not like this.
When the world's most brilliant mathematician (or at least one of the most brilliant) says "it would be rather bizzarre if your argument worked" the implications are absolutely clear.
As a scientist I would never make such a statement, moreso for a theory I admittedly don't understand.
Tangentially, it's not Tao's case, but I have seen a lot of bullying in the academia along these lines... "I am not saying it's wrong, just very bizzarre", "I am not saying it's wrong, but my Ph.D. student worked on it for two years and couldn't solve it", "I am not saying it's wrong, actually I don't even understand the details, but please recheck everything..." etc...
Euler identity looks very bizarre if you don’t understand the proof. Why should exponentiation, the imaginary unit and pi be related?
In mathematics there’s absolutely no place for judging the bizarreness of statements, either they are right or wrong, and of course such a judgement cannot be made by someone who admittedly doesn’t have the necessary background.
As I already said, often in the Academia saying that a result is bizarre is a not-so-subtle way of implying something is wrong by appealing to authority.
