What is the best interpretation of this relationship?

This is rather a strange question. It is rather like saying if adverse things happen to you, you'll be depressed. If good things happen, you won't. On an obvious level, we would be crazy if we were happy about adverse events and miserable about good ones! In fact, the negative relationship between the number of positive emotional experiences and depressive symptoms is not the cause of depression.

Depression is an illness, a mental health problem, not just the understandable misery after an adverse event. In depression, the individual cannot see the positives in his/her life: his/her outlook is pervasively pessimistic. Loading a depressive with wonderful treats is not the way to pull them out of that unfortunate state.