The dean's word is good enough to have answered no on AMCAS, and to similar questions on secondaries. However, Pfitzer goes deeper, and you cannot honestly answer no to THEIR question. It's not really clear what exactly happened in your case - what did you intend your friend to do with the password that one time, and what did he instead do over and over? I can't really think of something that is only unethical if you do it repeatedly, so I'm confused as to why the dean seems to feel your actions are innocent, yet your friend's are not, when his only offense was doing it more than once behind your back. =/
At the end of the day, it doesn't matter. The fact is, all applicants are expected to be ethical - while some betray that obligation and lie on their applications (and therefore have no business being doctors, but that's another story), plenty of others (including myself) come fully clean on everything the schools request...and so should you. In your case, it seems fair to say that you were investigated for such and such charge, but ultimately the dean himself concluded you were not at fault, and advised you to not represent yourself as such. Feel free to provide detail if you feel it necessary to explain what happened, but keep in mind the difference between honesty and self-crucifying. If you feel the truth reflects poorly on you, period, then your only honest option is to not apply to Pfitzer, and any other schools that are so demanding.
Yeah, I'm being tough, but on the other hand, I'm also being real. When it comes to people who advise you to pay attention to merely what's on the record, ask yourself: do you really want to entrust such lice with your intimate medical information? Do what you know is right.