You're both using separate and internally-varying definitions of racism.
I like your definition of racism per an inherent superiority test. Let's keep it. It operates on the level of ideas in your formulation, but it's really an element of an idea and better applied to individuals and, when colored by law, institutions. Antiracism thus holds its water as an ideology that seeks to e.g. remove that color in law.
Where it breaks down is when we reverse that antiracist ideology to the level of individual action and subtly amend the definition of racism from a racial superiority test to e.g. ignorance of systemic harm. Someone disagreeing with the statement "America is a racist country," or "persons are either anti-racist or racist" is not suggesting "one racial group is inferior to or superior to another racial group in any way." Yet if we brand that disagreement as racism, then antiracism becomes opposing not only that disagreement, but also the people disagreeing. If we go one step further and notice that many people espousing those views share a common race, and then lay animus collectively on their doorstep, then yes, the antiracist impulse becomes, itself, racist (by the superiority test and the axiom that racism, circularly defined, is an inferior belief).