Well, the wikipedia article suggested that it was because they believed she was responsible for Orestes's "unwillingness to reconcile with Cyril". That suggests they were provoked by the content of whatever she was saying to Orestes so if it had been for anything mathematical or philosophical, it was not recorded that way but I don't think there is a lot of evidence to go that route.

Here is a blog post by a historian about a movie that dealt with the subject, if you have the patience to read through it all. http://armariummagnus.blogspot.com/2009/05/agora-and-hypatia...