I have a good friend who doesn't celebrate Christmas, before she became by good friend I wished her a Merry Christmas, and she said, thank you for the good wishes, I'm Jewish so I wish you a a happy Hanukkah. We both laughed, but the spirit of our good wishes for each other was not lost in the choice of what holiday one choose to celebrate.
You and your friend have it right! You are both being who you are and that is the best it gets. Good for you and Merry Christmas and a blessed and prosperious New Year. No one should be offended at honesty.