[throwaway4233]

Based on the comments you have shared and the limited context I have, I believe that they understand that you are comfortable with the language and can build feature X if it is what is asked of you. However based on the `large company` emphasis in one of the comments, it could be because they expected your code to be maintainable, extendable or because it might be even lacking tests. In case the code you showcase meets the above given the time constraints you have, then move onto your next interview and do not worry about it. There a lot of factors involving interviews that do not relate at all to you and you should try not to be bothered by advice(white lie) that does not provide any value.