Probably a rejection. Interviews are not considered final admissions decisions, if anything they're just the beginning. You might still be considered for their regular MD program though.
Don't double post, pick a forum for your post and stick to it or the mods will arbitrarily shut down one of your threads.
Now that I have gotten my mean rule yelling out of the way to answer your question:
My interview invite came by e-mail. I am not sure how rejections are beng sent. Keep your head up, they will still consider you for MD even if they reject you MD/PHD and you have some great interviews all ready lined up!