Were I an interviewer I would not like that answer. No matter how much better you know Perl, there are generic valid reasons to write in Python instead that you can give that interviewer:

1. A personal project to help you learn Python, some Python library, etc. (Note, learning how a framework in another language does something is an excellent way to open your mind to new ways to do it in Perl.)
2. An existing Python project has a lot of the functionality you need, and extending it looks easier than rewriting it.
3. The team that will have to support and maintain it are Python developers rather than Perl developers.
4. A client is willing to pay you to write in Python, and is willing to accept your reduced productivity.

What you're trying to demonstrate with these answers are that you are open to working with others, fitting yourself to an organization's needs, and learning. The answer you gave instead could leave the impression that you have none of those traits.

The only time I would want to leave an interviewer with those types of negative impressions of me is if working with a particular language was so distasteful that I really don't want a job where I have to do that. The only language that I feel that way about is VB. Certainly I don't feel that way about Python. Furthermore Python has some good features that I wish were in Perl. For instance Perl has nothing equivalent to Python's list comprehensions and generators.