another example of the two-sided aspect of this civil war. Others who were also there that day claim he DID shout Torygg to pieces. One of those things we will never know for certain, but must take one person's word over anothers.
Two people confirm Ulfric's story, most other named characters don't comment on it, even if they were there. Not that it's relevant for this discussion. Because true or not, most people believe he did and that would be enough to create a law...
A rather useless law, because there would have been only one person capable of the Thu'um at that time, and that person would be Ulfric, and you'd think they could arrest him for other things besides shouting in a city.