The purebread horse is not a typo, it is a long standing typo joke that is part of our community culture. Feel free to ask around about it many will be familiar with ZRO who originally made the "mistake".
As for "an historic", there are 2 minds about the usage of A or AN before the word historic. I will refer you to this page for more info. Essentially it isn't wrong or right, it is simply a writing choice.
Thank you for taking the time to report them, however!