The second is probably more accurate - when beans are uneven in colour in themselves they are often described as 'tipped' (scorched). But some bean origins, due to varying size etc roast more unevenly overall - giving an uneven or patchy looking roast. Normally doesn't impact on flavour though.
However - some more aggressive roasters (fast, unmodded poppers for eg) can give this results too - even with beans that can be roasted much more evenly with a slower, more gentle roast (say KKTO). Just the nature of hot spots/ slow mixing etc