I too was at the Open House with DJ and others. I could answer some of your questions.
No they are not your advisor. They are just some faculty who work in a related area and can help answer any question you have about Cornell. Cornell is very flexible about picking advisors. You are not tied down to a professor or area. Rather they give you time till the end of the third semester to decide who your advisor will be. They actually encourage you to work with different people (for e.g. by doing courses which have a small research project involved..) in your first year and to gage what your interests are. Similarly your area of concentration too is not decided outright, and you have flexibility in that aspect too. Given your interests someone like Bobby Kleinberg, Jon Kleinberg or Eva Tardos maybe of interest to you, as they are all primarily in theory but are sound in ML as well.
As I mentioned above, students generally do small projects with multiple professors before they choose an advisor. If you were asking about co-advising, then some of the faculty I spoke to, were open to the idea. Also since Cornell has a breadth requirement as well, it is likely you will work with someone outside your concentration. Plus you would have an advisor in your minor discipline as well.
I also noticed a earlier post on funding. Since I'm also from India, and have been given my funding info, so I doubt that is the reason you have yet not been told about yours. Rather I think the specifics (TA or RA) will be decided close to start of the semester. From what I understood after speaking to students is that most students TA in their first semester, unless they have spoken to a faculty who is willing to take them on as an RA.