I had this same scenario happen to me! My chair invited me to meet with him to discuss the interview trail. When we started the meeting he prefaced the discussion saying that it was confidential and he takes no notes, so as not to remember details about which programs I specifically liked more or less than my home program. Next thing you know, he gets into "what are people saying about our program on the interview trail." I felt like I was now some inside investigator! To make it worse... halfway through our discussion the PD from our program joins us and he tells my #1, which isn't my home program!! So much for "confidential" huh? Then ANOTHER faculty member is invited in at the tail end of our meeting.
I definitely felt set up. They all stated that I was a strong enough applicant that them knowing where I rank them won't affect how they rank me... but I'm not convinced at all. I felt in some ways it may have been a violation, but I'm not going to do anything about it because they also offered to call people they know at my #1.
Basically, that long story is because I want you to learn from my example (i.e. mistake)! Maybe you should set the meeting up after February 25, so what you say can't be held against you for ranking.
I don't think that face time with a chairperson or program director during residency application is a bad thing, and is actually a good thing. I think the PD/chairman really did want to know about how their program looked compared to others on the trail. I wouldn't mention everything wrong with your home institution's program, but mention its pluses mostly and a couple of well known negatives that you heard on the trail.
They probably wanted you to be happpy to give information to your home institution about what they could do to get more applicants/look more attractive for residency.
Honestly if it was me and then I was asked about what my top choice was I would make generally vague comments about what programs I liked the best, what I liked about the home institution's program. The rank lists are not due for a while, so who know's?, you might change your mind about what is your number one after a second look. No need to give out "numbers". If asked what my number one is I would just laugh and say that I am still pondering how to construct my rank list and ask for pointers about what I should consider.
You shouldn't trust anyone to have your interests/rights at heart and never assume anything is confidential in medicine. Doubtlessly if you say that you won't rank your home program highly to the chairman and want to go somewhere else because of x,y and z, then they might try to change x,y and z and probably wouldn't rank you even though it is "confidential." What does that mean anyway? Confidential to him, the faculty or the program?
You should realize that the whole "Don't worry its confidential I won't write it down . . . " was a ploy to get you to reveal something you wouldn't otherwise have.
It is nice that the chair offered to call up people he knew at your number 1, he must have realized that you felt fairly certain you wanted to go there and felt comfortable telling him. Such calls can supposedly help a great deal, maybe he was trying to do you a favor if you are a really excellent student.
I don't think this meeting was premeditated, maybe poorly though out as the chair wanted to know what was going on and people in power rarely hear the bad news or the word on the street. . .