(start) <- A <- B <- C <- D <- E
1. make a branch at "start", i.e. at the previous of A
2. cherrypick A C D onto it
3. diff your branch with "start".
They discuss a problem in the article where you want to see the sum of diffs from separate branches and it's not clear which change should be diffed first, or what if they conflict.
This problem is solved using this branch/cherrypick/diff method because the order in which you cherrypick the commits is the order you'll see in the diffs; if you don't like that order, do the cherrypick in a different order.