Both words, “extremist” and “right-wing”, have no real hard definitions.
Is being socially conservative right wing? Is supporting capitalism right wing? Is inertia right wing? Is being progressive and, for example, anti-racist and pro-trans left wing? Is socialism left wing? Is only communism left wing?
What about extremism? Is someone an extremist if they condone violence? Is someone an extremist if they seek to change the system fundamentally? Is someone an extremist if their political beliefs are very strongly held, no matter what they might be?
Since these terms have no real definitions, it’s just shit-slinging.