I think the more accurate comparison is that the owner sent you a C&D saying you're banned from the restaurant, and then you try to say "oh, I though the C&D didn't apply any more because the waitress let me in." Would anyone seriously believe that?

The law applies to people, not computers. The only question is: did Linked In convey its revocation of hiQ's implied license in a way a reasonable person would understand? The computer code is only relevant if a reasonable person would take the HTTP status code to take precedence over the C&D letter.