Both are correct. The differences arises from the different spellings between America and Britain. English letters from these two countries vary a little bit. For example, honor (America) and honour (Britain).
Burned is how it is written in Britain and the countries colonized by it while Burnt is written that way in America.
As a person who grew up learning Britain's language, it was more of a confusion to come cross similar words with one letter missing or somehow changed but same meaning.