It wouldn’t take a genius to guess that a loner who eats lunch by himself might be off by himself.
This also doesn’t preclude somebody being set up after the fact *because* he was unaccounted for.
Since I believe that Lee himself created the staged attempt on JFK..... He would have known that he need to stay out of sight during the period that he was supposed to be shooting at JFK. And that's just what he did....However the conspirators thought that he would stay out of sight on the sixth floor where his body would have been found after the assassination ...But Bonnie Ray Williams fouled up that idea....