Wrong isn't quite the right word. GoT is not set in Medieval Europe, so by its very nature it can't be historically accurate. What was the historical Westeros like? Whatever George R R Martin wanted it to be like. The issue arises when people start assuming that it is an accurate depiction of the Medieval world. It is not. It's an amalgamation of times and cultures woven together to give an interesting cultural and political background to a fantasy story. So when people start asking, well did X happen in the Middle Ages, or assuming that GoT is "accurate" we often have to point out that whatever it was did not, or is an adaptation of something similar, or never ever happened. Medieval Europeans didn't commonly use morphine, for example, never used Ravens to send messages, etc.

You might be interested in previous threads on the relation of the Game of Thrones TV show and the A Song of Ice and Fire book series to medieval history:

#General Comparisons

• What common medieval fantasy tropes have little-to-no basis in real medieval European history? - 263 comments, over 10 months old.

• There is an exhaustive list of questions posed by the original poster which is met by an equally exhaustive list of answers by a flaired commenter with many followup questions and comments branching off from it.

• Were the Middle Ages anywhere near as violent as the TV show 'Game of Thrones'? - 166 comments, over 10 months old.

• Flaired commenters here get into an extensive debate on which historical time period and place Game of Thrones is most accurately compared with and if it should be compared in such a manner owing to the show setting's unique geographical concerns and fantasy elements.

• How believable are the setting and events in A Song of Ice and Fire? - 36 comments, over 2 years old.

• Commenters here make some comparisons from specific time periods and events in the Middle Ages and the books and show in question, as well as debate the merits of the "feudal" system in a landmass the size of Westeros.

• What aspects of life in middle ages Europe do movies always get wrong? - 499 comments, less than 1 month old.

• The OP actually references Game of Thrones in the post text, and the commenters go on to discuss differences in lighting, medicine, and accents from what is found in Medieval Fantasy works.

• What wrong ideas about medieval Europe might one get from popular works of "medieval fantasy"? - 513 comments, over 1 year old.

• Commenters here discuss in detail common errors in cuisine, body size, lighting, combat, medicine, and other issues.

• What were brothels really like in the medieval period? - 163 comments, over 1 month old.

• In the comment thread descending from the topmost comment, a flaired user discusses the difficulties of figuring out such information from the primary sources available due to specific biases and limited coverage inherent in said sources.

• Where do we get our idea of this medieval fantasy setting?(first time poster) - 29 comments, over 1 year old.

• This thread goes into the origins of Medievalism in the Victorian Era and how it shaped modern representations of the Middle Ages.

What time period does Game of Thrones / A Song of Ice and Fire most resemble or borrow the most inspiration from?

• Given the technology, political institutions, and social structures in the Game of Thrones series, which century does it most closely resemble? - 96 comments, over 1 year old.

• This thread picks apart individual elements from the types of armor used by the knights to the political situation at large and associates each of them with the most appropriate time period.

• What area of history would you recommend to a fan of A Song of Ice and Fire? - 10 comments, over 2 years old.

• Commenters here pull out specific periods and places from Ancient and Medieval Europe as well as one from China.

• Does A Song of Ice and Fire (Game of Thrones) base it's story on any historical events? - 12 comments, over 1 year old.

• This thread associates many events and groups in the show and books with their possible historical inspirations but does not lead to any major analysis of either the history or the fantasy.#Did X from Game of Thrones / A Song of Ice and Fire exist in Medieval Europe?

This is Part 1 of 3.

Part 2 of 3 deals with specific comparisons between George R.R. Martin's works and Medieval history in aspects such as warfare, politics, and daily life.

Part 3 of 3 deals with miscellaneous topics such as the comparing the prevalence of rape, finding historical counterparts to the Iron Bank of Braavos, discussing the beauty (or lack therof) of Medieval royal women, and cases of royal incest.

The most prominent thing for me is presentism. For example when Tyrion refused to consummate his marriage with Sansha, he said he will not rape her. Calling marital rape as rape is a very modern concept, most countries did not make it a crime until very recently. In the Middle Ages, the Decretum Gratiani stated that: "neither a wife may make a vow of abstinence without the consent of her husband, nor the husband without the consent of his wife”.