try pulling in hostvars?

roles/detect_archiso/tasks/main.yaml

@@ -6,3 +6,8 @@
 - name: inspect archinstall result
   set_fact:
     archiso_detected: "{{ which_archinstall.rc == 0 }}"
+
+- name: load alternate host vars
+  include_vars:
+    file: "../../../inventory/host_vars/{{ hostname }}.yaml"
+  when: archiso_detected and hostname is defined