As already answered by @Danielillo, enfadado is most likely the word your friend had in mind, although enojado is a perfectly proper word to use.
The use of Spanish and its words is incredibly diverse, as it is spread throughout multiple continents. Duolingo teaches a somewhat neutral Spanish. It tends to use the words that are more common in Latin America. The proper word for you is going to be the one used wherever you would like to speak Spanish. If your goal is to speak with people like your friend, please listen to the nitpicks they might mention to you, otherwise disregard it. Duolingo can be a bit awkward at times but Spanish is one of their top languages; they're most likely not going to have a blatant error on such a high profile language.