I had a good buddy who was an animal in the gym. He had the most shredded 8 pack year round (genetic freak) and he was convinced that the "uneven abs" look was due to people always crossing their leg during crunches, dips, pull ups ect from the time they started lifting. He never crossed his legs while lifting or he would switch up which foot was on top halfway through each set.
Pretty sure that would classify as "bro science".... But it stuck with me and always do the same lol.
Summary: pretty sure it's just genetics.