I am applying for a PhD program at the University in the US. I was contacted by one supervisor who after reviewing my PhD application material, thought that I am suitable to join his research team and he would like to discuss it more with me through a zoom meeting. However, I am not interested in his research and am considering rejecting his invitation.
My question is that: if I said that I reject his invitation, will this be a signal that I will be rejected by the Uni?
It would depend a bit on the field, but for most US applications to doctoral programs it is a committee that decides and a candidate only chooses an advisor after admission.
The exceptions are some lab sciences where admission to a lab might be necessary to be admitted, but those are rare. You seem to be in mathematics in any case, where it is unlikely that you need an advisor to be admitted.
It is possible that you were contacted by a junior faculty member, looking to boost their own local position by taking on students. There is nothing wrong with saying that you want to keep your options open at the moment.
Your first task in a US program will likely be to pass qualifying examinations in any case, not begin dissertation research in the first days.
See: How does the admissions process work for Ph.D. programs in Country X?
