It ss because Buryecs has a lower fixed rate and a higher floating rate – to the benefit is the two difference added together.
In the Keshi question, Keshi has a higher fixed rate and a higher floating rate – so the benefit is the difference between the two differences.
However, although the final answers to both questions are correct, I prefer to deal with swaps the way that I explain my free lectures which is more logical and I think easier to understand, as opposed to just learning a rule which is far too dangerous for a paper at the level of the AFM exam.