Можно явно добавить order by
"""
def get_search_results(self, request, queryset, search_term):
queryset, use_distinct = super(ProductAdmin, self).get_search_results(
request, queryset, search_term)
search_words = search_term.split()
if search_term:
equal_qs = queryset.filter(
name__iexact=search_term).order_by('brand')
obj_to_exclude = [o.id for o in equal_qs]
contains_sq = queryset.filter(
name__icontains=search_term).exclude(
id__in=obj_to_exclude).order_by('brand')
queryset = list(chain(equal_qs, contains_sq))
return queryset, use_distinct
"""