I doubt that he would be athletic. How do you remove the fat without damaging the body, the liver, the kidneys and other organs?
He could starve. That wouldn't make him athletic at all.
Or he could exercise like crazy, becoming athletic along the way and, incidentally, ALSO happening to lose weight.
However let us consider it differently.
If I am carrying a 30 kg backpack for a week of hiking and I suddenly take it off I have a spring in my step. I bounce into the air.
If I train on a 20 kg mountain bike and then, on race day, use an 8kg bike I feel so powerful it gives a psychological edge.
In other words even a fat person can be fit and athletic but they are hamstrung by their body mass.
If those people lose mass then they ARE athletic. They always were.
But an unfit slob is not going to become athletic just because they lose fat alone.