It's not weird, it's hard to get rid of that last bit of fat, you need to be under 10% Body fat for good definition in the abs and all around. In my pic I'm about 12% Boyfriend roughly and the top 4 come out easily but the last 2 you can barely see. When I drop down to about 10% it'll be perfect but that's hard for me to sustain.
I usually end up around 13% Boyfriend if I just workout once in a while and don't watch what I eat too much. If I want to drop BELOW 10% I really have to watch what I eat, the last bit is the hardest to lose.
All guys have different genetics as to where they put their fat. If you get your body fat down too low it can be unhealthy. I really doubt that is you, it looks like the model did tons of dieting to get that lean. I wouldn't recommend being 4% body fat.