Exclusive evidence – ‘or’ means only one
Quirk 93 (Randolph, Professor of Linguistics – University of Durham, and Sidney Greenbaum, “A University Grammar of English”, http://grammar.ccc.commnet.edu/grammar/conjunctions.htm)
OR To suggest that only one possibility can be realized, excluding one or the other: "You can study hard for this exam or you can fail." To suggest the inclusive combination of alternatives: "We can broil chicken on the grill tonight, or we can just eat leftovers. To suggest a refinement of the first clause: "Smith College is the premier all-women's college in the country, or so it seems to most Smith College alumnae." To suggest a restatement or "correction" of the first part of the sentence: "There are no rattlesnakes in this canyon, or so our guide tells us." To suggest a negative condition: "The New Hampshire state motto is the rather grim "Live free or die." To suggest a negative alternative without the use of an imperative (see use of and ): "They must approve his political style or they wouldn't keep electing him mayor."