He was not “just an instructor.” You are applying the ranks and categories used in 4-year universities and colleges, where instructor marks non-tenure track and assistant/associate/full professor marks tenure/track and tenured.
Law schools are different. You can’t simply transfer the ranks and categories. They have special categories for professional reasons.
He was offered tenure/tenure-track and turned it down, more than once. He did not want an academic career.
Sure, he was offered it out of affirmative action, but he was offered it. The rank he had was in between “mere instructor” and tenured professor.
Sure, UC says he was offered tenure track, but that is something easy to say retrospectively. If he was offered, it was likely with a proviso of ...and, uh, Barack, we do expect some academic writing from you. Which he knew he couldn't do. So a claim of an offer is devoid of any meaning whatsoever.
And Lecturer is, anyway you look at it, a far from lofty position in any academic setting.