I find the rumors about WashU being a hypercompetitive environment (and the entire notion that it's a numbers ***** -- but I've got my own theory on this) a fascinating aspect of SDN. It's something that is perpetuated throughout the premedical forums, but there's little to no evidence it's true from actual students. Of course, I may be biased, because there's a huge chance I'll be there next year, but I'll give you my perspective. I would venture that in many ways, WashU is less competitive than many other medical schools. The students there are excellent and have worked incredibly hard throughout undergrad. From the friends I have there (many, many!), the students seem to be very laid back, especially in their first year -- partly blowing off steam from undergrad, and probably partly because the quality of their institution protects them from needing to be competitive. After all you don't need to graduate AOA and top quartile of your class at WashU to do well in match placement, whereas that's not as much the case at a "lesser" known school.
The students I know and interact with are very happy at WashU, and most are very collaborative and social. I don't personally think there's any reason to be concerned. Good luck at your interview, and don't allow SDN rumors to bias your expectations/experience.