He does it so the fast one gets the hogs attention then when the bigger slower one gets there the hogs attention is on the first bulldog. This is typically how I run 2 catch dogs the better cd is turned loose 2nd so it has a better chance to get a good hold on the hog.
I never thought of it this way...but it sounds reasonable...
back when me and my brother hunted together we sent the slower one first and the faster bulldog second and we tried to time it so that they made it there at the same time...