No, it's not
IRB is an independent administrative tribunal that is responsible for making well-founded and fair decisions on immigration and refugee matters, efficiently and in accordance with the law. Established by an Act of Parliament, the IRB decides on refugee applications made by individuals who land in Canada and make an asylum claim to be in need of protection.
You can have an independent board and still be part of the government department of immigration, refugee and citizenship of Canada. There are so many departments and services under IRCC.