git checkout -b BRANCH_NAME creates a new branch and checks out the new branch while git branch BRANCH_NAME creates a new branch but leaves you on the same branch.
In other words git checkout -b BRANCH_NAME does the following for you.
git branch BRANCH_NAME # create a new branch
git switch BRANCH_NAME # then switch to the new branch
As per your screenshot where all three commits are listed, notice the merge commit (where author is max). So you merged back max_games branch into master from UI hence a new commit i.e merge commit was added to the master branch. So eventually there were two commits in the master branch add stories and the merge commit.
Since as per question you were not supposed to merge the max_games branch into master branch and it was clearly mentioned to have a single commit only
so it was supposed to be failed, I hope it clears your doubt now why this task failed for you.