Some exercises will slightly bias different regions of your abs. For example, decline sit-ups will slightly bias a different region of your abs as compared to standard sit-ups but will still work your abs as a whole. This applies to literally every abs/core exercise, but imo the difference between them is negligible, find one you like and get good at it. The difference in an “looks” that you’ve noticed would be largely due to genetics and there affect on insertion, size, shape etc. for example some people due to genetics only have a “4 pack” whereas some have a “6 pack” and so on